Effects of T-activin and a-tocopherol alone and together on lipid peroxidation (LPO) and carbohydrate metabolism are studied in rats with streptosotocin diabetes (male rats, n=102). Antioxidative activity of T-activin is compatible to that of a.-tocopherol. The antioxidative effect of combined therapy with both agents is more expressed than of monotherapy. T-activin normalized LPO and glycaemic values and increased blood plasma insulin level, which can be regarded as the onset of reparative regeneration of insulin-producing cells; v.-tocopherol did not notably increase the level of insulin or normalize blood glucose level. Thus, T-activin is characterized by a wider spectrum of therapeutic effects in experimental diabetes than a tocopherol.