We evaluated the response of white-tailed deer (WTD) (Odocoileus virginianus) to dietary aflatoxin. Fourteen 4-to-5-mo-old WTD were used in this 8-wk study, conducted between November 1993 and January 1994. Seven animals received a ration containing 800 parts per billion (ppb) total aflatoxin (AF). Seven control animals received the same ration without AF. At 0, 1, 3, 6 and 8 wk, feed consumption, feed conversion, liver enzymes, bile acid levels, and immune function via lymphocyte proliferation assays and delayed type hypersensitivity reactions were determined. At the conclusion of the 8-wk feeding trial, deer were euthanized and necropsied. Clinical illness was not evident in any of the animals, but by the end of the study, AF-fed deer had reduced feed consumption and body weight as compared to control deer; the differences were not statistically significant. The AF-exposed group had a significant increase (P = 0.03) in serum bile acid concentration as compared to control deer. Two AF-exposed deer had gross and histologic hepatic lesions indicative of a mild degenerative hepatopathy. Residues of an aflatoxin metabolite, aflatoxin M₁, were found in the livers of all treated animals. No differences in immune function were detected between the two groups. We conclude that consumption of 800 ppb AF in the diet of young WTD over an 8-wk period can produce subclinical hepatic injury.