Effects of onychiol B on smooth muscle were investigated on the isolated guinea-pig ileum. The inhibitory effects of onychiol B were tested by using the response to direct and indirect stimulation by drugs on the longitudinal contraction of guinea-pig ileum before and after blocking the nervous activity. In addition to the inhibitory effect, onychiol B also provoked irregular phasic contractions on steady preparations. The irregular contractions were overwhelmed by papaverine, but not suppressed by hyoscine. Therefore, it is suggested that onychiol B also has direct excitatory effects on smooth muscle.