Both nitrendipine and captopril have been shown to reverse left ventricular hypertrophy in hypertensive patients. So far, no study allowed a true comparison of these drugs in this regard and with respect to their potential of reducing circadian blood pressure. Therefore, a total of 86 patients with newly diagnosed arterial hypertension and echocardiographic evidence of left ventricular hypertrophy underwent randomized treatment with captopril (n = 43) or nitrendipine (n = 43). Eighteen patients had to be put on a combination therapy of nitrendipine and captopril during the course of the study to control blood pressure effectively. Before and after the 6th and 38th weeks of treatment all patients underwent ambulatory 24-hour blood pressure monitoring, M-mode echo assessment of left ventricular mass and Doppler evaluation of left ventricular filling. The 24-hour blood pressure data were smoothed with a Fourier series and then compared with a normotensive reference profile with respect to blood pressure load and variability. The daytime and nighttime mean and the office blood pressure were also analyzed. Substance-specific profiles of action were obtained by subtracting the smoothed profiles after therapy from the profiles before therapy. After 38 weeks ambulatory blood pressure had decreased from 152 ± 11/ 101 ± 7 to 137 ± 13/87 ± 10 mm Hg on nitrendipine and from 147 ± 11 / 99 ± 6 to 134 ± 13 / 89 ± 9 mm Hg on captopril. The substance-specific profiles calculated for captopril and nitrendipine showed a balanced antihypertensive effect throughout the day and the night. The mean percentage decrease in left ventricular muscle mass under nitrendipine was 15 % and did not differ significantly from the decrease of 21% under treatment with captopril (p < 0.001). There is no significant association between the reduction in blood pressure and the regression of left ventricular hypertrophy. In patients with disturbances of left ventricular diastolic function the early-to-late diastolic left ventricular flow ratio and the isovolumetric relaxation time were improved independent of the drug used. It is concluded that a long-term therapy with captopril and nitrendipine leads to a comparable degree of circadian blood pressure reduction and regression of hypertensive left ventricular hypertrophy.