An alkaloidal extract of Banisteriopsis quitensis (Niedenzu) Morton was tested using a rabbit ileum preparation, and inhibition of contractions was noted in untreated strips as well as in those treated with most known stimulants of strip motility. This action was additive with the effect of agents that inhibit strip motility. The activity of the extract was dependent upon intact supplies of calcium in the strip and was diminished by procedures causing depletion of calcium concentration. Loss of calcium from the strip was associated with a pharmacologic response to the extract.