We determined serum CK-BB mass concentration using a specific RIA method, in 267 patients with carcinoma confirmed histologically distributed as follows: 46 prostatic adenocarcinoma, 52 lung neoplasies, 70 colon carcinoma, 52 breast carcinoma and 41 gastric carcinoma; and also in 135 patients with histologically proved non-neoplastic diseases distributed as follows: 28 prostatic hyperplasy, 31 lung tuberculosis, 29 inflammatory bowel disease, 27 fibrocystic mastopathy and 20 gastroduodenal ulcer. Reference values in healthy subjects (n = 360) were 5.46 +/- 2.68 (SD) ng/ml. We found that serum CK-BB mass concentration is not a specific tumor marker but it is a valuable indicator of responsing to therapy and metastatic widespread. However, in prostatic carcinoma--prevalence 0.25, predictive positive value (PPV) 0.51 and predictive negative value (PNV) 0.88--and breast carcinoma--prevalence 0.32, PPV 0.60 and PNV 0.87--serum CK-BB can be used as a tumor marker. Only 12 over 268 patients with different neoplastic disease (4.47%) showed detectable serum CK-BB catalytic concentrations.