In order to evaluate the use of Doppler echocardiography in the assessment of the haemodynamic effects of antihypertensive drugs, the acute haemodynamic response to felodipine and additional administration of metoprolol after 90 min was assessed in 10 hypertensive patients, by using both the Fick method and Doppler blood flow velocimetry in the ascending aorta. Intrabrachial artery pressure was significantly reduced by the treatment. Both the Fick and Doppler estimates of cardiac output (CO) rose significantly with felodipine and reached their highest values after 30 min, 45 ± 8% (s.e.m.) and 58 ± 7%, respectively. The felodipine-induced increase of heart rate (HR) persisted for 90 min, but the increase of stroke volume was only transient. Metoprolol brought CO and HR back to control levels. The felodipine- and metoprololinduced changes of CO and stroke volume (SV) from control were on average not different between the observations with the Fick and the Doppler techniques throughout the study. As for the absolute values (control period), the Doppler measurement underestimated SV (10 ml) and CO (1.1 l/min) in comparison with the Fick method, and the limits of agreement (mean difference ± 2 s.d.) between both methods were 42 and —22 ml for stroke volume and 3.4 and —1.2 l/min for CO. In conclusion, despite the poor agreement in absolute results between the two methods, aortic Doppler velocimetry reflects the acute haemodynamic changes induced by felodipine and metoprolol in a group of hypertensive patients. The technique should facilitate the study of haemodynamic effects of drugs in man.