Blood samples were collected from 40 white-tailed deer (Odocoileus virginianus) from 4 winter yards in northeastern Minnesota from 17 March 1974 through 23 April 1975. The results of 26 blood assays were examined for the effects of age, sex, capture date, capture method, disease and location. Age-related effects were found for serum chloride, calcium, gamma globulin, creatine phosphokinase (CPK), lactic dehydrogenase (LDH), and alkaline phosphatase. The only sex difference was lower CPK in males. Date of collection effects were found for erythrocyte count, mean corpuscular volume (MCV), serum glucose, and nonesterified fatty acids (NEF A). Capture method affected serum glucose, acid base balance, and serum enzymes. Effects related primarily to capture location or habitat differences were found for erythrocyte count, MCV, mean corpuscular hemoglobin concentration (MCHC), serum urea, cholesterol, LDH, thyroxine, and NEF A. Animals whose assays indicated the poorest nutritional status inhabited wintering areas with the oldest vegetation. Habitat differences can be detected by measuring the physiological status of the local animal populations.