(FORTUNE Small Business) – Venture 135 rugged miles west of Kathmandu into the village of Besisahar, and you'll encounter a carriage suspended from a taut wire, safely whisking villagers over one of the treacherously swollen rivers that career through the Himalayan foothills in the monsoon months. More than 4,000 Nepalese use one of 29 such wire bridges each day to attend school, say, or get medical attention. The bridges are the brainchild of entrepreneur David Sowerwine, 65, and his wife, Haydi, 64. "There were many unnecessary deaths and injuries before the bridges," says Sowerwine, who left the Bay Area in 1991 to lead a USAID program in Nepal. The Sowerwines fell in love with the country and five years later started EcoSystems to build rural-transport products. The licensing of its technology, government contracts, and grants cover the $15,000 cost for each bridge. The five-person company has grossed $296,000 in sales but turned a profit only once in eight years. It is not just about business, says Sowerwine, explaining why he accepts the company's meager returns. "Changing the lives of these rural people has become personal." --JOSEPH MATTERN