Twenty-one male and female adults 43 +/- 4 yr of age completed in 8-wk control period, 16 wk of conditioning, and 12 wk of deconditioning to determine whether exercise alters blood pressure. Subjects were classified as borderline/mild hypertensive (H, diastolic pressure greater than or equal to 85 and less than 104 mm Hg, N = 8) or normotensive (N, diastolic pressure less than 85 mm Hg, N = 13) based on average blood pressure during the control period. Conditioning increased (P less than 0.05) VO2max to a similar extent in both groups (average, 14%) and decreased (P less than 0.05) resting heart rate (H, 78 +/- 5 to 65 +/- 3; N, 75 +/- 3 to 71 +/- 3 beats.min-1). The double product over 24 h of ambulatory monitoring of blood pressure and heart rate decreased (P less than 0.05) in both groups. After deconditioning, VO2max returned to values not different (P greater than 0.05) from those of the control period. Ambulatory 24-h double product and heart rate increased (P less than 0.05). In spite of this strong evidence of a conditioning effect, neither group showed changes (P greater than 0.05) in average 24-h ambulatory or casual blood pressure. The average ambulatory blood pressure for 8-h segments of the day (8 a.m.-4 p.m., 4 p.m.-12 a.m., and 12 a.m.-8 a.m.) was also not altered. Cardiac output and total peripheral resistance at rest did not change (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)