Growth hormone is a powerful anabolic hormone that affects all body systems and plays an important role in muscle growth. It is released from the anterior pituitary in response to a variety of stimuli including exercise, sleep, stress, and the administration of a variety of drugs and amino acids. Serum levels are variable and are dependent on such factors as age, sex, body composition and level of fitness. Animal experiments have shown that growth hormone can partially reverse surgically induced muscle atrophy and weakness. Growth hormone administration to normal animals leads to muscle hypertrophy, but this muscular growth is not accompanied by increased strength. Growth hormone excess leads to acromegaly, a disease with significant morbidity, including a myopathy in which muscles appear larger but are functionally weaker. Although there is no scientific evidence documenting an improvement in athletic performance following growth hormone supplementation, it is reported that this practice is becoming more widespread among athletes wishing to avoid detection with current doping control measures. There are anecdotal reports that athletes are injecting cadaveric or biosynthetic forms of growth hormone, both of which are associated with potentially serious complications. In addition, some athletes are ingesting drugs and amino acids in the belief that their endogenous growth hormone secretion will be increased. There have been no scientific studies on the effects of growth hormone supplementation, and the anecdotal reports have been equivocal, with some individuals reporting spectacular results while others report no change. Despite the lack of valid evidence for its efficacy and its potentially serious side effects, it has been predicted that growth hormone use may increase. Growth hormone use and abuse has the potential to dramatically change the future conduct of athletics and may prove to be a threat to the concept of fair competition.