In Hungary the use of angiotensin converting enzyme inhibitor enalapril has emerged as one of the most important drugs in the treatment of hypertension. The aim of our study was to evaluate the antihypertensive effect of enalapril of Hungarian production in combination therapy and alone, according to sexes, to the body mass index, among smokers and non smokers as well as non diabetic and in patients with diabetes (IDDM and NIDDM). The diurnal blood pressure values were registered by a 24 hour ambulatory blood pressure monitor. During the 6 weeks of the enalapril therapy (n = 28) both the daytime (141/84 vs. 135/80 mmHg) and the night-time (130/78 vs. 124/72 mmHg) blood pressure values decreased; the increase of diurnal indices during the therapy (SI/DI 6/8% vs. 8/10) reflect the 24 hour long lasting effect of the drug. The body mass index had no influence on the efficacy of treatment. Our results indicate that enalapril manufactured in Hungary is an effective antihypertensive drug both in monotherapy and in combination, in both sexes (especially in men), irrespective of the body weight, in non-smokers and especially in smokers, in insulin dependent and in non-insulin dependent diabetes mellitus alike.