1. The effects of the specific angiotensin II receptor type I (AT1) antagonist candesartan on renal proximal tubular sodium transport were studied using lithium clearance. The effects of candesartan on mean arterial blood pressure (MABP), renal plasma flow (RPF), glomerular filtration rate (GFR) and sodium and potassium excretion were also investigated. 2. Male Wistar rats were anaesthetized with Inactin (thiobutabarbital sodium; Sigma, St Louis, MO, USA). Clearance markers (8% polyfructosan, 1% para-aminohippuric acid and 4 mmol/l lithium chloride) were given into a jugular vein at the rate of 1.6 mL/h per 100 g bodyweight. Candesartan was given as bolus injection (0.01, 0.1, 0.2, 0.5 and 1.0 mg/kg) followed by 60 min continuous infusion at a rate of 0.5, 5, 10, 25 and 50 microg/min per kg, respectively. 3. The non-depressor dose of candesartan (0.01 mg/kg) did not alter RPF or GFR, whereas diuresis, natriuresis and kaliuresis were observed. The higher doses of candesartan reduced MABP, RPF and GFR, although diuresis, natriuresis and kaliuresis were still observed. 4. Renal tubular sodium and water reabsorption were inhibited after intravenous administration of candesartan independently of an alteration in arterial pressure. Lithium clearance data indicate that the site of inhibition was in the proximal nephron segment.