Relaxin has been reported to influence gastrointestinal motility in mice. However, at present, nothing is known about the effects of relaxin on the electrophysiological properties of the gastrointestinal smooth muscle. In the present experiments relaxin, other than influencing the colonic motility pattern, has been shown to act on cell membrane properties. The results of the present study indicate that relaxin directly modulates the motility of the proximal colon and the membrane potential of smooth muscle.