To explore the relationship between selenium deficiency in cancer and nutritional factors, we measured the serum concentrations of selenium in 1978-1983 in patients with gynaecological cancer (N = 277) and correlated these with the estimated daily intake of selenium, which varies in Finland depending on the proportion of selenium-rich imported grain. The selenium concentration increased significantly from 1978-1979 to 1982 in the series of all cancer patients (p less than 0.001) and separately in cases of cervical (p less than 0.001) and endometrial cancer (p less than 0.02), parallel to the increased daily intake of selenium. The serum level of selenium decreased in 1983, when the import of selenium-rich grain was reduced. Low serum selenium in cancer patients thus seems to be mainly dependent on dietary factors.