To investigate the effects of an acute bout of exercise on total and free insulin-like growth factor-I and insulin-like growth factor binding protein-3 plasma concentrations, 32 healthy elderly subjects (67-80 years, 16 men) performed a strength test, which consisted of two sets of 12 repetitions at 12-repetition maximum and four sets of 5 repetitions at 5-repetition maximum for horizontal leg press, seated chest press, and bilateral leg extension movements. Ten out of the 32 subjects served as time controls. Blood samples were drawn prior (08.30 h), immediately (10.30 h), and 6 h (16.30 hours) after the strength test in exercising and resting subjects. The 32 subjects were then randomly assigned to habitual physical activity or to an 8-week strength training program. After 8 weeks, both sedentary and trained groups underwent blood samplings under the above-mentioned conditions. The exercising group showed increased total and free insulin-like growth factor-I concentrations immediately (+17.7 and +93.8%, respectively), and 6 h (+7.5 and +31.2%, respectively) after the test, whereas no significant changes in insulin-like growth factor binding protein-3 concentrations were observed in either exercising or resting control groups. Strength training induced no significant changes in baseline insulin-like growth factor-I and insulin-like growth factor binding protein-3 concentrations. Trained and sedentary groups showed similar hormonal response pattern to the strength test, which consisted of increased total and free insulin-like growth factor-I concentrations. The data indicated that strength exercise can induce an early and sustained insulin-like growth factor-I release, in elderly subjects, regardless of their training status.