Blood pressure falls after a single session of exercise. The duration for which this fall in blood pressure persists is not known. Sustained hypotension after a single session of exercise may have important implications in the treatment of patients with mild hypertension. We studied 24 subjects (12 normotensive subjects and 12 patients with mild or borderline hypertension). Blood pressure was measured in the laboratory for 30 minutes before and for an hour after graded bicycle exercise to maximal voluntary capacity. Subjects then left the hospital and measured their blood pressures at home (three measurements every 2 hours) following a strict measurement protocol for the rest of the day (usually between 8 and 12 hours). These home blood pressure measurements were compared with home blood pressure measurements recorded at the same times on a nonexercise control day. At 30 minutes after the graded maximal exercise test, the hypertensive patients experienced a fall in blood pressure from 142 +/- 3.5/93 +/- 6.5 mm Hg (mean +/- SEM) to 124 +/- 4.5/79 +/- 2.8 mm Hg (p less than 0.01). For the normotensive subjects, blood pressure after exercise fell from 117 +/- 3.1/70 +/- 2.1 mm Hg to 109 +/- 3.1/62 +/- 2.8 mm Hg (p less than 0.01). Despite these striking blood pressure reductions for the second half hour after exercise, blood pressure measurements recorded at home were not significantly different on the exercise and control days in either group. We conclude that although a single bout of exercise lowers blood pressure for a short (1-hour) period, this hypotension is not sustained.