Cisapride, a substiuted piperidinyl benzamide that is chemically related to metoclopramide, is a prokinetic agent that facilitates motility of the gastronitestinal tract (1). The mechanism by which cisapride exerts its actions is not clear. It enhances acetylcholine release in the myenteric plexus of the gut, and evidence exists that it has an agonistic action on a serotonin receptor, probably the 5-HT4 receptor (2). The drug is well tolerated, and no central nervous system side effects have been reported. We describe two patients with parkinsonism who experienced aggravation of tremor while on therapy with cisapride.