In the present study the prescription patterns and cost of antihypertensive drugs in two outpatient clinics, located in two different countries (Zürich, Switzerland, and Münster, FRG), were analyzed from 1975 till 1985 by using representative random samples of hypertensive outpatients. Throughout the observed period the leading positions were held by diuretics and beta-blockers, whereas central sympatholytics and ganglion blockers nearly disappeared. A rapid increase in the use of calcium antagonists occurred within the last 2 analyzed years. Drugs in fixed combination containing reserpin showed a constant decrease during the observed period, whereas beta-blocker-containing combination drugs increased in both clinics. The comparison between the two clinics revealed only minor differences in the prescripton pattern of the various known classes of antihypertensive drugs. However, marked differences were observed within given classes between the preferred products. Both in Zürich and Münster the mean annual drug cost per patient doubled from 1975 to 1985. Especially during the last few years these changes took place with a remarkable rapidity, obviously the result of a more intense promotion of new antihypertensive drugs.