Hyperglycemia in diabetes induces oxidative stress and generates reactive oxygen species (ROS). Melatonin may influence diabetes by regulating insulin secretion and providing protection against ROS. H2S contribute important role in pathogenesis of several diseases and influence on the activity of glutathione system. The experiments were carried out on 50 sexually mature male albino rats with the body weight – 0.16–0.18 kg. Alloxan diabetes was evoked via single injecting the rats with 5% alloxan monohydrate solution in the dose of 150 mg/kg. The animals were divided into subgroups: (1) control rats; (2) alloxan diabetic rats with overt; (3) animals with overt diabetes were introduced the melatonin intraperitoneally in the dose of 10 mg/kg at 8 a.m. daily during 7 days. The research showed that alloxan diabetes decrease H2S level on 45%. Increased content of reduced glutathione (G-SH) in rats with diabetes is probably induced by enhanced regeneration of the oxidized form in the blood of rats of this group. The activity of glutathione reductase and glutathione peroxidase was higher than in intact ones. The introduction of melatonin promoted normalization of the level of basal glycaemia in diabetic animals indicating hypoglycemic action of melatonin administration. In the blood of alloxan diabetic rats receiving melatonin increases the content of H2S and normalizes some indices of glutathione system.hem.