OBJECTIVE This study was performed to assess the acute effects of the new angiotensin II antagonist, candesartan cilexetil, on systemic and renal haemodynamics in patients with sustained essential hypertension [diastolic blood pressure (DBP) 95-114 mmHg]. METHODS After 4 weeks of placebo treatment, systemic and renal haemodynamics were investigated in 17 patients with a mean age of 62 years and a mean systolic and diastolic blood pressure of 170/98 mmHg, just before (baseline) and for 4 h after administration of a single oral dose of candesartan cilexetil, 16 mg. Plasma concentrations of candesartan (the active compound formed from the pro-drug candesartan cilexetil), angiotensin II (Ang II), as well as plasma renin activity (PRA), were measured before and after dosing. RESULTS At 2, 3 h and 4 h after dosing with candesartan cilexetil, systolic blood pressure (SBP) and DBP, as well as mean arterial pressure (MAP), were significantly lower than at baseline. The mean reduction in MAP 4 h after dosing was 8.8 mmHg (-6.5%). This effect was due to a fall in total peripheral resistance (TPR), while heart rate (HR), stroke volume (SV) and cardiac output (CO) were virtually unchanged. After 4 h there was a marked reduction in renal vascular resistance (RVR) of 0.0273 mmHg x ml(-1) x min (-16%), resulting in an increased renal plasma flow of 64.9 ml x min(-1) (14%). The glomerular filtration rate was increased by 7.75 ml x min(-1) (8%), and the filtration fraction (FF) was not significantly changed. There was no apparent relationship between the changes observed in systemic and renal haemodynamic variables and plasma concentrations of candesartan. Plasma renin activity increased over the study period, but in general the patients had low PRA. Changes in plasma concentrations of angiotensin II were inconsistent between patients. CONCLUSIONS A single oral tablet of candesartan cilexetil, 16 mg, induced systemic and renal arterial vasodilatation and blood pressure reduction, without compromising renal perfusion or filtration or affecting cardiac performance. Plasma renin activity which was low in general, increased over the study period, but changes in plasma concentrations of angiotensin II were inconsistent.