Selenium has been suggested to have chemopreventive properties and also have anticarcinogenic potential. Meanwhile selenium may influence the metabolism of certain heavy metals and chemical carcinogens. In a case-control study of breast, colon and prostate cancer, a total of 1048 cases and 688 population-based controls, matched for age and gender were studied. Of these a total of 501 cancer cases and 202 controls produced toenail sample for their selenium concentrations. For the cadmium, mercury and arsenic content of the toenail samples, we used neutron activation analysis method. None of the correlations between level of selenium and its three antagonists, namely arsenic, mercury and cadmium in the toenail of the mentioned cases and controls were statistically significant. We also observed that there were no significant differences between cases and control regarding the cadmium, mercury and arsenic level of the toenail. This study indicates that it seems there is no correlation between the level of selenium and its antagonist heavy mineral, of toenail concentration among cases of breast, colon and prostate cancer and their matched controls.