LYNNE MARSHALL says she has never fully understood why HSBC Holdings, one of the world's largest banks, would send 2,000 employees on far-flung environmental expeditions. But Ms. Marshall, who was among the first to be chosen, is not second-guessing her employer.

"This was a dream of a lifetime," said Ms. Marshall, 42, an HSBC vice president and trust account officer — and an archaeology buff. She spent two weeks in July excavating animal bones and sifting sediment to help researchers study early man in Venta Micena, Spain, all at HSBC's expense. "I just can't believe I had this opportunity."

Ms. Marshall, from the HSBC office in Buffalo, is part of an uncommon experiment. HSBC, which is based in London, announced early this year that it was donating nearly $50 million to the Earthwatch Institute, WWF (formerly known as the World Wildlife Fund) and Botanic Gardens Conservation International for conservation projects worldwide over the next five years. It is by far the largest donation HSBC has ever made, and by far the largest that any of the three groups has received.

But this corporate philanthropy is particularly unusual because HSBC employees like Ms. Marshall are spending two weeks at a time traversing jungles and glaciers and battling the elements, all in the name of environmental science. All told, HSBC and Earthwatch estimate that the 2,000 employee "fellows" will contribute in five years what might typically take the usual number of field workers on these projects 100 years to accomplish. And when they return from these research trips — which are coordinated by Earthwatch — the employees are expected not only to make presentations to colleagues, but also to create a related project in their home communities, using grants from HSBC.

By year-end, 210 employees will have participated, on trips to Brazil, Iceland, Sri Lanka, Australia and dozens of other places to help scientists study ecological systems and human civilization. An additional 290 will follow next year, with 500 more in each of the remaining three years. Earthwatch is getting $16 million to cover employee expenses and grants to scientists, and HSBC estimates that it will absorb an additional $4 million in costs associated with taking employees away from their work.

WWF is receiving $18.4 million to restore and protect several major river basin habitats. Botanic Gardens Conservation International will use its $11.6 million to protect endangered plant species and pay for botanical education programs.

The first group of HSBC employees to go on Earthwatch expeditions included 16 from the United States and was selected from nearly 2,200 applicants. Of HSBC's 170,000 employees, about 110,000 speak fluent-enough English — a requirement — to be eligible. Earthwatch chose the fellows; the bank doesn't see the applications, which ask employees to explain why they want to go and how they plan to share what they learn.

HSBC says the program is part of what it called a longstanding commitment to environmental and educational philanthropy projects. The company is a major corporate donor — its philanthropic spending totaled $30.6 million in 2001. Until this year, however, HSBC had focused on local programs in the 81 countries and territories in which it operates, never exceeding $2 million or $3 million for a single project.

"The environment is something that people feel very strongly about, and the reality is that we can make some difference there because of our scale," said Amanda Combes, the HSBC manager who oversees HSBC's community programs, including this latest venture, which HSBC calls Investing in Nature.

Ms. Combes, who is based in London, said the Earthwatch component, especially, showed the staff "that this is not just a perk, but a true demonstration that we as an organization take the environment seriously, that we're not just doing this as window dressing."

Not everyone agrees that HSBC has a pristine record as a corporate citizen. It has underwritten bonds for the World Bank, which antiglobalization advocates accuse of having economic policies that undermine human rights and the environment in developing countries. And HSBC has made investments in socially and environmentally contentious projects in places like China and Indonesia, financing, for instance, nuclear plants and, in China, the Three Gorges Dam, which critics maintain will destroy the environment in the Yangtze River region. ISIS Asset Management, a London investment firm that monitors socially responsible investing, said in a recent report that HSBC was in its "chasing pack" category — meaning that the bank had made progress assessing the environmental impact of its lending policies but still had room for improvement.

HSBC has allowed its Investing in Nature partners to scrutinize its investing and environmental policies and has agreed to set up joint committees to monitor progress. The bank also has hired KPMG to review its operations and set targets for lowering greenhouse gas emissions (through reduced utilities use and business travel), water consumption and waste production. Looking ahead, HSBC "will not automatically disengage from specific industry sectors," according to a company report on its behavior as a corporate citizen, but it will "err on the side of caution if we think the environmental risks of a transaction outweigh the benefits."

Earthwatch and the scientists it finances agree that HSBC's philanthropy, notably its donation of employees, has substantial impact. "This project, this type of research, wouldn't exist without the volunteers," said Peggy Rismiller, an environmental physiologist who studies threatened animal species on Kangaroo Island off southern Australia.

Like other scientists who rely on Earthwatch grants, she uses volunteers to gather data and do the grunt work that may become tedious for a researcher or a student. But to volunteers, it can be exhilarating. "Volunteers bring such enthusiasm; they'll go out and work and do the job until it's completed," Ms. Rismiller said.

Earthwatch sends out about 4,000 research volunteers each year, most of whom pay their own way or find sponsors for their trips. The organization has been setting up employee fellowships for about 10 years, for companies like Starbucks, Royal Dutch/Shel and Rio Tinto, a large mining company. But HSBC's program sends out more employees each year than all of the other employee fellowships combined. "The effectiveness of something like this is vastly increased when it's concentrated," said Steven D. Lydenberg, a principal at Domini Social Investments, which focuses exclusively on socially responsible investing. "That's really making a substantial commitment that more general volunteer programs, while they end up supporting employees, don't have."

HSBC employees who have made the trips cannot quite believe that this is one of their perks. "I had never met people like this before," said Diane Abbott, 36, a branch manager in Rochester who traveled to Brazil in March to help scientists monitor jaguars and conduct a tree census in the Pantanal wetlands. "I felt so far removed from the life I normally lead. Even after a couple of days, it felt like I hadn't sat at a desk, driven a car, run into a store in five years. It really did give me an entirely different perspective."

Ms. Marshall said she was so taken with her archaeological dig in Spain that she had a hard time pulling herself away. "I'll tell you, I could have stayed there another five or six months," she said.

Darryl Szarpa, 49, who works in facilities administration in Buffalo, related similar feelings. He said his trip in August to Canyonlands National Park in Utah, where he trapped invertebrates and amphibians as part of an ecological survey, inspired thoughts of a second career once he retires.

EMPLOYEES relished their work, even when the going was rough. "There were just levels of physical discomfort that I wasn't prepared for," said Emily Zahniser, 31, who traveled to central Ontario in July to study the effects of logging and development on ancient forests. Ms. Zahniser, who works as an executive assistant for HSBC in Manhattan and is an avid hiker and camper, battled mosquitoes and heavy rains while bushwalking through dense spruce and brush. "Had I known what I was getting into, I might have been hesitant, but now, having done it, there's no way I would have walked away," she said.

Ms. Zahniser applied for a forestry project because of her interest in Inwood Hill Park, which contains the remnants of primeval forest in Manhattan. For her community project, she would like to bring children to the park's ecology center and share what she has learned. Others have ideas for a mock archaeological dig, an Earth Day fair and plant-identification lessons for schools.

Peter Etu, 62, a senior programmer and technical analyst in Buffalo, returned in August from excavating a bison kill site in Jackson Hole, Wyo. Now he is thinking about his community project — and is glad it's required. "I think if we didn't have that component, we'd do our fellowships and most of us would stop," Mr. Etu said. "This is an impetus to carry on."