Immunoreactivity for p53 and c-erbB-2 proteins was studied in 31 schistosomal urinary bladder carcinomas and 21 cases of schistosomal cystitis with hyperplastic, metaplastic and/or dysplastic (premalignant) lesions. The results were compared with 30 carcinomas and 21 premalignant lesions of the urinary bladder without schistosomiasis. Abnormal nuclear p53 protein accumulation was found in 17/31 schistosomal and in 15/30 non-schistosomal carcinomas and in 8/21 schistosomal cystitis with premalignant lesions of which five showed hyperplasia. No case of non-schistosomal hyperplasia or squamous metaplasia examined showed p53-positivity. In non-schistosomal carcinomas p53 positivity was significantly associated with tumour grade (grade I-II vs grade III tumours: P = 0.021) and greater age (P = 0.004) while in schistosomal carcinomas no such associations were found. Cytoplasmic membrane-bound positivity for c-erbB-2 oncoprotein was found in comparable percentages in schistosomal and non-schistosomal bladder carcinomas (10%), and in both groups was co-expressed with p53. p53 gene alteration is an important event in the development of both schistosomal and non-schistosomal bladder carcinoma.