The purpose of this study was to investigate whether continuous infusion of an anabolic steroid, stanozolol, would alter skeletal muscle size and performance in sedentary male mice. The study was performed as a preliminary to an investigation on the effect of anabolic steroids on skeletal muscle regeneration in the mdx mouse, an animal model used for the study of Duchenne muscular dystrophy. Skeletal muscle structure and contractile behavior, and heart, liver, kidney, and testis wet weights were assessed after 3 or 6 wk of continuous exposure to one of two concentrations of stanozolol. Continuous release pellets containing either a high (1.5 mg) or low (0.5 mg) concentration of stanozolol were implanted into 8-wk-old C57BL/6J male mice. Control mice were implanted with pellets containing the drug vehicle. Stanozolol infusion had no significant effect on the contractile strength or mass of either fast-twitch extensor digitorum longus or slow-twitch soleus muscle. The resistance to fatigue of both muscles, assessed in vitro, was unaffected by stanozolol; however, postfatigue recovery of soleus twitch and tetanic tension after 3 wk of treatment was significantly (P < 0.05) increased in high-dose mice compared with control and low-dose mice. Androgen-sensitive muscles, bulbocavernosus and levator ani, were significantly (P < 0.05) increased in wet weight after 3 wk of stanozolol treatment, but were not significantly different from control muscles after 6 wk, suggesting that continuous infusion produced a tolerance to the drug. Similarly, heart wet weight was significantly (P < 0.05) increased in stanozolol-treated mice compared with control after 3 wk, but not after 6 wk. Testis wet weight was significantly (P < 0.05) decreased in low-dose mice compared with control mice at 3 wk, but not at 6 wk. Plasma testosterone concentration was not significantly different between any of the groups after 3 or 6 wk of treatment. This study suggests that in the absence of other factors (e.g., high-intensity exercise or other degenerative changes in muscle fibers), continuous infusion of an anabolic steroid produces no significant effect on the growth, contractile strength, or endurance of hindlimb skeletal muscles.