Hydrogen peroxide-induced chemiluminescence of red cells of various age groups in diabetics was under study. A clinical, laboratory, and instrumental examination of 15 patients with diabetes mellitus was carried out. Red cell fraction chemiluminescence was examined in quantum metric equipment with FEU-39A and FEU-140 radiation detectors sensitive to the visible and UV regions. Intensive fluorescence of the third and, in some cases, of the fourth red cell fractions was observed in the diabetics, in contrast to the reference group of normal subjects (more than 3-fold higher in the patients). A high level of peroxide chemiluminescence observed at the end of examinations of the third and fourth fractions of the diabetics' red cells is an evidence of a high concentration of lipid peroxidation products in the diabetics, increased vs. the norm. Diabetes mellitus involves activation of the red cell fraction free-radical processes, leading to a preterm destruction of functionally active red cells first of all.