Sporulated oocysts of Eimeria acervulina were administered orally to cage-housed broilers at a dose of 3.5 X 10(5) resulted in mild subclinical coccidiosis. Clostridium perfringens incorporated in feed at a level of 2.5 X 10(8) organisms/g. produced lesions characteristic of necrotic enteritis. Mortality of 8% (7/80) occurred in birds fed a ration inoculated with Cl. perfringens alone. Mortality of 35% (28/80) was observed in birds which received an oral dose of E. acervulina and which were fed simultaneously with a ration containing Cl. perfringens. Birds which were fed an inoculated ration two days after an oral dose of E. acervulina showed 41% (33/80) mortality. Birds which received an inoculated ration for two days before administration of an oral dose of E. acervulina demonstrated 18% mortality (15/80). Birds which were fed an inoculated ration four days after an oral dose of E. acervulina showed 10% mortality. Infection with E. acervulina reduced the pH of intestinal contents with a simultaneous depression in serum protein. A 39% increase in intestinal passage time from 178 to 248 minutes occurred on the fifth day after infection with E. acervulina. These experiments suggest that necrotic enteritis, attributed to proliferation of a toxigenic strain of Cl. perfringens, followed intestinal stasis and minimal lesions induced by mild intestinal coccidiosis.