The addition of Dianabol (17alpha-methyl-17beta-hydroxyandrosta-1,4-dien-3-one) (1 mg/100 g of diet) to a diet containing raw field bean (Vicia faba L.) as the sole source of protein has been studied in young male rats, fed for two weeks on the legume diet, as compared to casein-fed animals. A significant improvement (p less than 0.02) in the biological value and net protein utilization was found in the rats fed the legume diet with Dianabol added. Furthermore, a significant reduction (p less than 0.02) in the non-protein nitrogenous fraction of the skeletal musculature, together with a significant rise (p less than 0.02) in the sarcoplasmic and myofibrillar nitrogenous fractions of this musculature, was found in the rats fed the raw legume diet with Dianabol added. Serum insulin levels, significantly reduced (p less than 0.02) in the legume-fed rats, reached the values of the control group by the addition of Dianabol to the legume diet. The possible nature of these effects is discussed.