The androgen receptor mediates the androgenic and anabolic activity of the endogenous steroids testosterone and 5alpha-dihydrotestosterone. Current knowledge of the androgen receptor protein structure, and the molecular mechanisms surrounding the binding properties and activities of agonists and antagonists has led to the design and development of novel nonsteroidal ligands with selected tissue-specific androgen receptor agonist and antagonist activities. The activity of these compounds, termed selective androgen receptor modulators (SARMs), is directed toward the maintenance or enhancement of anabolic effects on bone and muscle with minimal androgenic effects on prostate growth. SARMs are of potential therapeutic value in the treatment of male hypogonadism, osteoporosis, frailty and muscle wasting, burn injury and would healing, anemia, mood and depression, benign prostatic hyperplasia and prostate cancer.