1. The responses of the rabbit rectococcygeus muscle to stimulation of the extrinsic pelvic nerves have been investigated using intracellular micro-electrode recording techniques. 2. Submaximal pelvic nerve stimulation evoked a depolarization (e.j.p.) which was graded with stimulus strength and abolished by atropine (10(-6) g/ml.) and tetrodotoxin (TTX). 3. Single supramaximal stimuli evoked action potentials associated with muscle contraction. 4. In the presence of atropine, to abolish the e.j.p.s, supramaximal stimulation of the pelvic nerves evoked hyperpolarizations (i.j.p.s) which were graded with stimulus strength and abolished by TTX. 5. The transmitter responsible for the i.j.p.s is unknown. Phentolamine (10(-5) g/ml.) and propranolol (3 x 10(-5) g/ml.) in concentrations which block respectively alpha and beta adrenoceptors and the adrenergic neurone blocking agent guanethidine (10(-6) g/ml.) were ineffective in blocking the inhibitory response. 6. It is concluded that stimulation of the pelvic nerves to the rectococcygeus releases two transmitters, acetylcholine, responsible for the e.j.p. (and muscle contraction) and a non-adrenergic non-cholinergic transmitter which is the basis for the mechanical relaxation.