Boreal caribou (Rangifer tarandus caribou) are an ecologically and culturally important wildlife species and now range almost exclusively in the boreal forests of Canada, including the Northwest Territories, northern Alberta, and British Columbia. Boreal caribou are threatened throughout their Canadian range because of direct and indirect natural and anthropogenic factors. In the Northwest Territories, however, they have a continuous range that overall has not yet been subjected to the same degree of anthropogenic habitat fragmentation and degradation that has occurred elsewhere in Canada. To monitor the health of boreal caribou populations and individuals, we collected blood from 104 adult, female boreal caribou captured between March 2003 and February 2006 and measured serum biochemical parameters. Serum creatinine was higher in pregnant than in nonpregnant caribou. Several biochemical parameters differed among years, but they tended to be similar to those reported for reindeer. Serum antibodies were found to an alphaherpesvirus, Toxoplasma gondii, and to the Mycobacterium avium subspecies paratuberculosis in 37.5, 2.9, and 1.3% of boreal caribou, respectively. Fecal samples were collected from 149 boreal caribou, and Cryptosporidium sp. oocysts, Giardia sp. cysts, trichostrongyle ova, dorsal-spined nematode larvae, cestode ova, and Eimeria sp. were found. Trypanosoma sp. was detected in the blood of 72.1% of boreal caribou. Eimeria sp., Cryptosporidium sp., and Giardia sp. have not been previously reported in boreal caribou.