Young adult guinea pigs were studied 6 and 9 weeks after silastic capsules containing 5 alpha-hydrotestosterone (5 alpha-DHT) and methandrostenolone (Dianabol) were implanted. DHT was more effective in causing testicular atrophy and was apparently more androgenically potent in sustaining the size of the seminal vesicles. Both steroids led to hypertrophy of the masseter muscle and increase in gastrocnemius protein concentration. Cardiac tissue was sensitive to the effects of these steroids, particularly to the larger amounts of absorbed Dianabol, in terms of increases in DNA concentration and transient loss of tissue sodium, potassium, and calcium. All alterations in muscle composition occurred in the total absence of change in tissue water. Hypernatremia and hyperkalemia was present in steroid-treated animals with significant loss of urinary potassium in DHT-treated guinea pigs. Adrenal atrophy and the lowering of circulating cortisol was further indicative of effects upon adrenocortical function and the regulation of electrolyte balance.