SUMMARY— The incidence and intensity of schistosomal infection in 50 African malignant bladders determined by quantitative analysis have been compared with a matched control group of non-malignant cadaver bladders, and the incidence of radiological calcification in the former has been compared with that of 50 adult urinary bilharziasis patients without associated malignancy. Compared with 45% in the non-malignant group, schistosomal infection was present in an overwhelming 94% of the malignant cases. Radiological calcification in the malignant bladders (38%) was slightly more than in patients with urinary bilharziasis (35%). In the majority of the malignant bladders (55.3%) the parasitic infection was noted to be of moderate to low intensity. It has been suggested that the overall severity of schistosomal infection is unlikely to be the sole factor in the pathogenesis of carcinoma of the urinary bladder.