The effect of new antidiabetic drug Diabenol [9-diethylaminoethyl-2,3-dihydroimidazo-(1,2alpha) benzimidazol dihydrochloride] on life span and spontaneous tumor incidence in NMRI and transgenic HER-2/neu mice was studied. Female NMRI and transgenic HER-2/neu mice were given diabenol with drinking water (0.1 mg/l=approx. 10 mg/kg of b.w.) 5 times a week since the age of 2 months until natural death. The treatment with the drug failed influence body weight gain dynamics, food and water consumption and the body temperature in NMRI mice. Diabenol treatment slowed down age-related disturbances in estrous function and increased life span of all and 10% most long-living NMRI mice. The treatment with diabenol inhibited spontaneous tumor incidence (mammary gland and lymphomas mainly) and increased the mammary tumor latency. Dibenol treatment slowed down age-related changes in estrous function in HER-2/neu mice, failed influence survival of these mice and slightly inhibited the incidence and decreased the size of mammary adenocarcinoma metastases into the lung. Thus, long-term treatment with diabenol is safe and non-toxic in mice. The drug increases survival and inhibits spontaneous carcinogenesis in mice