Poultry products represent a significant reservoir of Salmonella typhimurium. Ochratoxin A, a mycotoxin and natural contaminant of poultry feedstuffs, produces detrimental effects on the immune and other systems of the broiler chick. Because poultry products are possible sources of S. typhimurium contamination that can potentially infect humans, there is a need to know whether ochratoxin A can alter the growth of Salmonella in poultry. We investigated the pathological alterations of young male broiler chicks by S. typhimurium in the presence (3.0 mg/kg) or absence of ochratoxin A in the diet. Ochratoxin A alone in the diet decreased the body weight and increased the relative organ weights of the liver, kidney, gizzard, spleen, pancreas, and proventriculus. It did not affect the heart and bursa of Fabricius. The mycotoxin altered the serum concentrations of proteins, enzymes, calcium and phosphate salts, normal tissue constituents, and catabolic metabolites in a pattern that would suggest damage to skeletal muscle, liver, kidney, pancreas, and bone. Birds fed diets containing ochratoxin A had microcytic and hypochromic erythrocytes and a decrease in phytohemagglutin- and concanavalin A-stimulated blastogenesis. Salmonella typhimurium alone had no affect on the variables measured except for a decrease in body weight. With the exception of an increase in mortality (13.2%, a significant synergistic interaction) and decrease in body weight, Salmonella in combination with ochratoxin A did not alter the values of the remaining variables measured from those measured in the ochratoxin A diet alone. Cecal colony count of S. typhimurium was not affected by treatment with ochratoxin A.