Three canthin-6-one alkaloids, canthin-6-one, 5 methoxycanthin-6-one and the novel alkaloid 1-hydroxy-ilmethoxycanthin-6-one have been isolated from the root bark of Brucea antidysenterica. The effects of piperine on the responses of the fruit-bat and guinea pig gastrointestinal tract smooth muscle to transmural nerve stimulation (TNS) were studied. Piperine (all concentrations) reduced or abolished the responses of the bat oesophagus, duodenum, rectum and the guinea pig stomach. Low concentrations enhanced the responses of the guinea pig oesophagus and ileum whilst higher concentrations produced inhibition. Bat ileum showed four types of responses to TNS: contraction plus relaxation; contraction only; relaxation followed by contraction and relaxation. The contractions were abolished by tetrodotoxin whilst the relaxations were resistant. Pipenne blocked the contractions but the relaxations were not readily blocked. It is concluded that piperine is a non-specific spasmolytic.