Male subjects (10 experimental, 16 control) with borderline hypertension (140/90 to 160/95 mm Hg) participated in a circuit weight training program for 9 wk to assess its efficacy and safety. Resting blood pressure and heart rate were measured under standardized conditions prior to and following each session and at several locations in the circuit. Subjects were assessed pre- and post-training. Upper and lower body strength increased 12.5 and 53% when assessed by one-repetition maximum lifts for bench press (57 to 64 kg) and leg press (134 to 205 kg), respectively. Total weight lifted per circuit increased 57% (4,374 to 6,866 kg). Lean body mass increased 2.2% (64.0 to 65.4 kg), skinfold thicknesses decreased, and other measures of body composition remained unchanged. Cardiovascular endurance as assessed by arm ergometry maximal oxygen uptake increased 21.1% (1.9 to 2.3 1 X min-1), and by 7.8% as assessed by treadmill maximal oxygen uptake (40.9 to 44.1 ml X kg-1 X min-1). Resting heart rate and systolic blood pressure did not change. Diastolic blood pressure fell from 95.8 to 91.3 mm Hg. All changes were significant to at least P less than 0.05. Thus, circuit weight training can elicit marked improvements in muscular strength and modest improvements in body composition and cardiorespiratory endurance. Circuit weight training does not exacerbate resting or exercise blood pressure and may have beneficial effects.