Sixty-five percent of the fecal samples collected from small rodents in the central Washington Cascades were positive for Giardia spp. Trapping studies showed that microtines of the genus Microtus were heavily infected with the parasite. Morphologically the cysts and trophozoites were of the G. duodenalis type. Small rodent populations appear to maintain their infection throughout the year. Data suggests that there is no difference in the percent of positive animals in areas receiving a lot of human use as opposed to those areas receiving very little or no human use. Giardia spp. was also found in elk and beaver samples. Campylobacter spp. was recovered infrequently from the small rodents inhabiting alpine meadows. Water voles were found to be susceptible to a human isolate of C. jejuni and to shed the bacterium for several weeks. The studies indicate that microtines and possibly other small rodents inhabiting mountain meadows have a potential to act as a reservoir for both Giardia spp. and Campylobacter spp. Because these animals may carry human pathogens they should be included in animal surveys designed to assess the health risks associated with mountain watersheds. (Copyright (c) 1987, American Society for Microbiology.)