We tested the hypothesis that free radicals play a role in the selective destruction of pancreatic beta-cells in BB/Wor rats. Diabetes-prone BB rats of both sexes and 40 days of age were divided into three groups. The control group was fed ad libitum Purina rat chow powder, while the experimental group was fed ad libitum the rat chow powder blended with a mixture of four known free radical scavengers: allopurinol, mercaptopropionylglycine, dimethylthiourea and Vitamin E. A third group was pair-fed 10 g chow powder/rat/day, since in earlier experiments we observed that rats on the experimental diet consumed only about 10 g/rat/day. All rats were studied up to age 120 days. Body weight and food intake were measured daily. Urine was tested for glucose beginning at age 60 days. When glucosuria appeared, blood glucose and urinary ketones were measured. Body weight gain in the experimental and pair-fed groups was similar, but lower than the control group. Life table analysis of the data showed a decreased and a delayed onset of diabetes in the rats fed free radical scavengers. Thus, the results of this study demonstrated that calorie restriction and the related impaired growth did not affect the incidence of diabetes in the BB rat. In addition, the results suggested a role for free radicals in the spontaneous destruction of pancreatic beta-cells in the BB rat.