We set out to establish a simple, reproducible, rat in vitro model of erectile function and to use this to demonstrate the functional importance of both neuronal- and endothelial-derived nitric oxide within this animal. Two corpora cavernosal smooth muscle strips were harvested from sexually mature male Wistar rats and mounted in an organ bath for measurement of isometric tension. Following contraction with noradrenaline the strips were relaxed by the addition of either acetylcholine or sodium nitroprusside. Electrical field stimulation was performed in the presence of atropine and guanethidine. Relaxation responses were repeated in the presence of methylene blue, L-arginine, L-NNA and haemoglobin +/- L-arginine. Methylene blue abolishes the relaxation to acetylcholine and EFS; L-NNA and haemoglobin cause a significant impairment in the relaxation response. L-arginine reverses the effect of haemoglobin. In conclusion, the inhibitory, relaxant stimulus of rat corpora cavernosa is due to both neuronal nitric oxide and endothelial-derived nitric oxide released in response to cholinergic stimulation.