The Rocky Mountain Biological Laboratory (RMBL) is an independent, non-profit field station with no institutional affiliation, which provides facilities to researchers who wish to study high-altitude biology in a field setting. Researchers have come to RMBL for six decades, and more and more long-term users are expressing an urgent need for currently unavailable high- quality laboratory space in order to enhance their research activities. This proposal will support construction of a sturdy, two- story, site-appropriate passive-solar laboratory building that will contain six individual lab rooms, a large multi-user room for shared equipment, and sanitary facilities. The building is designed for the harsh environment encountered at 2900 m elevation in the Rocky Mountains, and will be available for year- round use. The RMBL administration and members pledge an equivalent value of researcher housing construction and renovation, research equipment purchases, and other capital improvements as matching funds toward the cost of this new laboratory building.