In this study, the serum selenium (Se) levels in cancer patients (n = 101) and healthy controls (n = 101) were measured. The cancer group comprised the patients with the following primary site tumors: stomach (n = 10), colon (n = 10), larynx (n = 10), lung (n = 10), cervix (n = 10), ovary (n = 10), prostate (n = 10), breast (n = 10), bladder (n = 10) and other sites (n = 11). The mean (+/- SD) values for Se were found to be 94.1 mu g/l (+/- 12.5) in controls and 69.2 mu g/l (+/- 11.1) in the cases. Cases and controls were compared with respect to a number to potentially confounding factors: age, sex, quetelet index (kg/m(2)): smoking status, alcohol intake and dietary intake. Serum Se concentration was also discussed in connection with the specific site of cancer. According to this study, the serum Se levels of cancer patients were lower than the levels of healthy subjects.