The antidiarrhoeal activity of a procyanidin isolated from the bark of Sclerocarya birrea was studied, using four models of experimentally induced diarrhoea in rats. The cathartic agents used were: magnesium sulphate, castor oil, arachidonic acid and prostaglandin E2. At doses of 150 mg/kg, the procyanidin showed antidiarrhoeal activity in all the models of experimentally induced diarrhoea. The procyanidin (2.5 mug/mL-0.64 mg/mL) dose-dependently inhibited the phasic contractions of the isolated guinea-pig ileum spontaneous activity; this inhibition was significantly reduced by hexamethoniUM (10(-4) M). It also modified the dose-response curves to acetylcholine in a non-competitive way, and relaxed, in a dose-dependent manner, the contractions induced by acetylcholine (10(-7) M) and KCI (50 mm), being five times more potent against acetylcholine. The procyanidin modified the biphasic mechanical response evoked by acetylcholine (10(-7) m) in isolated guinea-pig ileum, inhibiting the phasic response more profoundly than the tonic one. It is concluded that the antidiarrhoeal activity of the procyanidin isolated from S. birrea bark is related to an inhibition in intestinal motility. The way in which it produces this inhibition can be related to an interference with the subsequent events evoked after muscarinic stimulation.