The effects of feeding diets containing ochratoxin A (OA) (2.0 mg/kg) and deoxynivalenol (DON) (16 mg/kg) singly and in combination were characterized in male broiler chicks from 1 to 3 wk of age. Body weight gains and efficiency of feed utilization were significantly reduced by feeding OA singly, DON singly, and the OA/DON combination. Increased relative liver, kidney, and proventriculus weights were observed in the OA and OA-DON groups and blood urea nitrogen (BUN) was increased in the DON group. Serum uric acid, creatinine, and triglycerides were significantly elevated, and total protein, albumin, cholesterol, and aspartate amino transferase (AST) activity were decreased in the OA group. Histopathological examination of the liver, kidney, spleen, proventriculus, gizzard, and bursa revealed that lesions were confined primarily to mild hepatocellular degeneration, with milk diffuse lipidosis of the liver and mild swelling of the renal tubular epithelium of the OA and OA/DON combination groups. For a few parameters such as efficiency of utilization and relative liver, gizzard, and spleen weights. OA and DON appear to interact additively. However, many of the parameters such as body weights, body weight gains, BUN, total protein, and AST show significant interactions that can best be described as less than additive or in some cases antagonistic.