Gender and age have distinct and interrelated effects on GH secretion in adults. GH secretion falls significantly with aging, particularly in women. The fall in GH release is amplitude- rather than frequency-modulated and appears to be related to estrogen status. Oral estrogen administration is unphysiological and causes a marked perturbation of the GH/insulin-like growth factor I axis. A nonparenteral route of administration is required for further investigations of the physiological role of estrogen in GH secretion.