The effects of ochratoxin A (OA) and vanadium (V), singly and in combination, were determined in male Leghorn chicks from 1 to 28 days of age. The chicks were fed a control diet containing the following additives: A) none; B) 2.5 mg OA/kg; C) 50 mg V/kg; D) 2.5 mg OA plus 50 mg V/kg. These data show that body weight gains were significantly reduced by OA and V singly, and a toxicity-enhancing synergism exists between OA and V, which caused a further reduction in performance. The OA-V combination caused a significant increase in the relative weights of the liver, kidney, gizzard, and proventriculus and a significant decrease in the relative weights of the bursa of Fabricius. This decrease in bursal weight was due to atrophy of lymphoid follicles as indicated by the increase in the histologic lesion score. Uric acid in serum was increased, and albumin, calcium, and phosphorus were decreased in the OA-V combination group. There were also small but significant changes in the hematological parameters measured. Distribution of OA to the liver and kidney was not altered, nor was the distribution of V to the liver, kidney, or muscle tissue. Histologic lesions in kidneys were mild but were more prevalent in chicks in the OA-V combination group.