The effect of 4 months of physical training on resting, exercise and 24-hour blood pressure (BP) was studied using a randomized crossover design in 26 healthy, sedentary men, with an average age of 39 +/- 10 (standard deviation) years. Peak oxygen uptake increased by 14% (p less than 0.001) and the physical working capacity at a heart rate of 130 beats/min by 25% (p less than 0.001). The heart rate was reduced by 7 beats/min at night (p less than 0.01) and by 6 beats/min during the day (p less than 0.001). Training-induced changes of BP varied according to measuring conditions. A decrease in BP at rest while sitting in the morning in the laboratory was significant for diastolic (-5 mm Hg, p less than 0.01) but not for systolic BP. During exercise, systolic BP was significantly lower after training, when measured at the same submaximal workloads. However, when workload was expressed as a percentage of peak oxygen uptake, systolic BP was not different before and after training. When measured during 24 hours, the training-induced change in BP was not significant at night either for systolic or diastolic BP. During the day the decrease in diastolic BP was significant (-5 mm Hg, p less than 0.001), but the change in systolic BP was not.