In 10 severe hypertensives the effects of intravenous administration of scalar doses of captopril were evaluated. The behaviour of blood pressure, heart rate, electrocardiographic pattern and left ventricular (LV) diastolic function, in basal condition (T0) and after 60 min of captopril infusion (T60), were analysed. Diastolic performance was assessed by pulsed wave Doppler echocardiography, evaluating transmitral peak flow velocities in early diastole (PEDV), late diastole (PLDV) and the PEDV/PLDV ratio. All patients showed an increase in LV mass (assessed by M-mode echocardiography) and altered diastolic performance, documented by high PLDV and low PLDV/PEDV ratio values. Clinical, haematological, urinary and biochemical data were also assessed for possible side effects. Captopril significantly reduced BP in 7 out of the 10 patients. Supine BP decreased from 212 +/- 15.3/126 +/- 5.6 to 171 +/- 17.7/98 +/- 11.8 mmHg (T0 vs. T60 P less than 0.0001). No electrocardiographic abnormality was observed during the study. The goal of antihypertensive effect was reached at 40-50 min after the onset of captopril therapy. Heart rate showed a small but constant decrease (from 76 +/- 7.7 to 72.8 +/- 5.7 beats/min, T0 vs. T60, P less than 0.05). Side effects of intravenous captopril were always mild and transient; no severe hypotension as 'first dose effect' was observed in our study. The echocardiographic data showed a significant decrease in LV end-systolic dimension after captopril infusion, while left atrial, LV diastolic dimension and fractional shortening remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)