Thirty-four untreated patients with essential hypertension WHO I-II, 17 patients under treatment with beta-blockade, and 32 healthy controls with a wide range of exercise capacity were studied at loadless pedaling (W0) and at the work load eliciting a blood lactate concentration corresponding to 4 mmol X l-1 (onset of blood lactate accumulation or OBLA). At W0 the treated patients had approximately the same systolic blood pressure (SBP) as the healthy controls, while the untreated patients had a higher SBP than the controls. At WOBLA the SBP was higher in the untreated patients than in both the treated patients and the healthy controls. On an individual basis it was found in the healthy controls and the untreated patients that the SBP at WOBLA showed a slight and insignificant increase versus SBP at W0, whereas the difference in SBP between WOBLA and W0 ("exercise SBP increase") demonstrated an inverse relationship (P less than 0.001-0,01) versus W0. It was suggested that for both healthy controls and untreated patients the exercise SBP depended on a "basal" level as depicted by W0 and a further SBP increase due to the exercise load. The difference between the two groups was that the patients with untreated hypertension displayed their relationships at higher pressure levels indicating the presence of a hyperkinetic drive. The treated patients appeared to have a lower increase in SBP between W0 and WOBLA than any other group, suggesting an unfavorable effect of the beta-blockade.