Selenium in serum and selenium and glycogen in erythrocytes were determined in diabetic patients divided into noninsulin-dependent (n = 50) and insulin-dependent (n = 31) groups according to the etiopathogenesis of their diabetes. Selenium was determined by the method of atomic absorption spectrometry. Serum level of selenium was statistically significantly different in patients with either noninsulin-dependent (59.23 +/- 12.2 microg/L) or insulin-dependent (58.23 +/- 16.7 microg/L) diabetes mellitus as compared with the control group of 62 subjects (64.2 +/- 11.5 microg/L; p < 0.05). There was no statistically significant difference in the serum levels of selenium between the groups of patients with noninsulin-dependent and insulin-dependent diabetes mellitus. The levels of erythrocyte glycogen were 2.0580 +/- 1.326, 2.0380 +/- 1.735, and 2.0036 +/- 1.3537 microg/g Hb in the control group, noninsulin-dependent group, and insulin-dependent group, respectively, with no statistically significant between-group difference. The decreased levels of selenium in serum and erythrocytes of diabetic patients suggest the possible role of glutathione peroxidase activity.