In order to establish reasons for a decreased yield of positive culture results from peritoneal dialysates of patients with continuous ambulatory dialysis peritonitis 60 specimens were examined, 47 (78%) of which were positive. A negative result was associated with a delay in processing the specimen and the presence of antimicrobial substances in the dialysate. The application of a method involving dilution of a large volume of effluent in broth did not substantially increase the positive yield.