Anabolic steroids have been widely recommended in the management of debility in association with the diseases of old age. Their action in promoting weight gain and in speeding rehabilitation is said to depend on nitrogen retention leading to increased muscle bulk reflected by increased fat-free mass (lean-body mass). In elderly patients undergoing rehabilitation a double-blind trial over 4 months of stanozolol, an orally active anabolic agent, is reported in which measurements of total body weight, body fat and fat-free mass were recorded. Physical activity and performance levels were also measured. Total body weight was found to have increased in both groups of patients, mainly due to increased body fat. There was no evidence of fluid retention due to the drug. Despite the absence of an anabolic effect, the group taking stanozolol increased their levels of physical activity significantly.