Histochemical studies carried out on sections of rat and guinea-pig prostate glands revealed the presence of acetylcholinesterase- and noradrenaline-containing nerve fibres in the fibromuscular stroma. Positive staining for acetylcholinesterase but not for noradrenaline was also seen in the epithelium. Electrical field stimulation with trains of 0.5 ms pulses, dial setting of 60 V, delivered at 1-30 Hz for 10 s at 5 min intervals, was applied to nerve terminals within the rat and guinea-pig isolated prostate glands. The evoked contractions were frequency-dependent. Tetrodotoxin (1 microM) abolished contractions evoked by short pulse repetitive stimulation (trains of 20 0.5 ms pulses at 10 Hz every 100 s) in tissues from both species. The field stimulation-induced contractions of the prostatic smooth muscle were markedly attenuated by guanethidine (10 microM) and prazosin (0.1 and 1 microM) indicating that neurotransmission to the prostatic smooth muscle in both species is predominantly sympathetic and noradrenergic, and that noradrenaline released during field stimulation acts at postjunctional alpha1-adrenoceptors. Atropine (0.1 and 1 microM) caused a slight but significant reduction of the field stimulation-induced contractions of prostate smooth muscle from both the rat and the guinea-pig. In the guinea-pig, cholinesterase inhibition by physostigmine and neostigmine, both at 10 microM, enhanced the field stimulation-induced contractions of the prostatic smooth muscle. This enhancement was reversed by atropine (0.1 microM) but not by hexamethonium (0.1 mM). These data are compatible with some participation of acetylcholine, acting at muscarinic receptors, in neurotransmission to prostatic smooth muscle.