In order to evaluate the action of captopril on left ventricular filling in hypertension, 14 hypertension (158 +/- 10/101 +/- 5 mmHg) patients aged 51 +/- 6 years were investigated by Technetium 99m gamma-angiography. The time/activity curve was used to determine the maximum filling rate (MFR) and maximum filling time (MFT) of the ventricle before and after treatment with captopril (mean dose : 44 +/- 26 mg/day for 7 months). Blood pressure was significantly lowered by treatment and there was a decrease in left ventricular mass from 128 +/- 17 to 118 +/- 15 g/m2 (p = 0.07). Maximum filling rate was accelerated by treatment from 2.27 +/- 0.57 to 2.57 +/- 0.43 VTD . s-1, p = 0.005). This variation was due essentially to half of the patients, suggesting an "all or nothing" type response. Maximum filling time did not vary. The basic question raised by this type of study is to know whether the improvement in the available relaxation parameter, MFR, was associated with actual improvement in filling, which is the true aim. Although the explanations offered for the observed findings are hypothetical, taking into account of all the trial data together with the morphological data provided by echocardiography suggests that captopril does have an actual and hemodynamically significant action on filling.