In order to evaluate the specificity of tumor markers in chronic renal failure, we have determined serum levels of carcinoembryonic antigen (CEA), carbohydrate antigen 19.9 (CA 19.9), carbohydrate antigen 50 (CA 50), alphafetoprotein (AFP), neuron-specific enolase (NSE), prostatic acid phosphatase (PAP), prostatic specific antigen (PSA), squamous cell carcinoma antigen (SCC), carbohydrate antigen 15.3 (CA 15.3) and carbohydrate antigen 125 (CA 125) in 30 patients with chronic renal failure and in 36 hemodialyzed patients without clinical evidence of neoplasia. CEA, CA 50, NSE and SCC frequently show increased serum levels, suggesting a renal metabolism, while others remain, generally, within the normal levels.