Serum selenium concentration (scSe) (microgram/l) was comparatively measured in healthy persons (n = 202), patients with colorectal adenoma(s) (n = 44) and colorectal carcinoma (n = 48). In patients with adenoma(s) scSe (59.05 +/- 15) was significantly lower (p < 0.001) compared with scSe in the control group (66.8 +/- 14.43). Hyposelenemia was more pronounced in patients with multiple polyps (n = 11) than in patients with single adenoma (n = 33) (p < 0.05). Patients with colorectal carcinoma had also significant decrease in scSe (50.93 +/- 13.81) compared with the control group (p < 0.001 and with the adenoma patients (p < 0.001). According to the analysis of variance, highly significant differences were found among the cancer patients stratified in Dukes' stages A to D (p < 0.001), indicating a strong negative correlation between extension of cancer and hyposelenemia. Furthermore, hyposelenemia seemed to be more pronounced in the mucinous type of carcinoma than in adenocarcinoma (p = 0.056). This results indicate that hyposelenemia is strongly associated with colorectal neoplasia (including extension and severity of the disease) and that it may not only be a result but also one of tumorogenic factors. That means that selenium supplementation could be important in prevention or even adjuvant therapy of colorectal cancer.