1. Postexercise hypotension (PEH) plays an important role in the non-pharmacological treatment of hypertension. It is characterized by a decrease in blood pressure (BP) after a single bout of exercise in relation to pre-exercise levels. 2. The present study investigated the effect of a single session of resistance exercise, as well as the effect of nitric oxide (NO) and the autonomic nervous system (ANS), in PEH in spontaneously hypertensive rats (SHR). 3. Catheters were inserted into the left carotid artery and left jugular vein of male SHR (n = 37) for the purpose of measuring BP or heart rate (HR) and drug or vehicle administration, respectively. Haemodynamic measurements were made before and after acute resistance exercise. The roles of NO and the ANS were investigated by using N(G)-nitro-L-arginine methyl ester (L-NAME; 15 mg/kg, i.v.) and hexamethonium (20 mg/kg, i.v.) after a session of acute resistance exercise. 4. Acute resistance exercise promoted a pronounced reduction in systolic and diastolic BP (-37 +/- 1 and -8 +/- 1 mmHg, respectively; P < 0.05), which was suppressed after treatment with L-NAME. The reduction in systolic BP caused by exercise (-37 +/- 1 mmHg) was not altered by the administration of hexamethonium (-38 +/- 2 mmHg; P > 0.05). After exercise, the decrease in diastolic BP was greater with hexamethonium (-26 +/- 1 mmHg; P < 0.05) compared with the decrease caused by exercise alone. 5. The results suggest that acute resistance exercise has an important hypotensive effect on SHR and that NO plays a crucial role in this response.