We studied the effect of haemodialysis on the serum levels of tumour markers in 78 patients, 49 men and 29 women with a mean age of 61 12 years, who had been undergoing haemodialysis for 39 f 10 months. No patient had any clinical evidence of malignancy. Serum values of carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), squamous-cell-carcinoma-related antigen (SCC), neuron-specific enolase (NSE), tissue polypeptide antigen (TPA), CA 15-3, CA 19-9, and among males prostate-specific antigen (PSA) were determined before and after dialysis. Postdialysis values, after being corrected for haemoconcentration, were compared with predialysis values. A significant increase of 32% was observed in NSE levels (P