Cisapride, a substituted piperidinyl benzamide, is a prokinetic agent which effects motility throughout the length of the gastrointestinal tract. Its novel mechanism of action is thought to involve enhancement of acetylcholine release in the myenteric plexus of the gut. In this study we investigated the effect of cisapride in idiopathic chronic constipated patients. Study group and control group were comparable with their sex, clinical findings and constipation time. There were no pathological findings in both groups with double contrast x-ray of the colon, tumor markers, rectosigmoidoscopy, occult blood stool and biochemical tests. After total gastrointestinal transit time was determined with Sitzmark’s radioopaque marker and a standard dietary list (1800 kcal with 50 g. fiber) was given to both groups, treatment was started. Each subject who had a stool frequency of less than 2/week and/or total gastrointestinal transit time of>72 hours, was randomly assigned to double blind treatment with either Cisapride (n:17) (10 mg.t.i.d) or placebo (n:17) (10 mg.t.i.d) for 8 weeks. Mean age of patients was 52.9 in cisapride group (16-68) (3 males 14 females) and 55.4 (37-78) in the placebo group ( 6 males and 11 females).Stool habits, laxative consumption and side effects were noted by the patients during the treatment time. At the end of 8 weeks these finding and total gastrointestinal transit time were reevaluated in all the patients. Cisapride decreased oro-anal transit time (OATT) from 152.47±34.92 hours t6 97.41±21.58 hours (p<0.05) and significantly increased stool frequency from l.47±0.62 to 3.50 ±1.77 per week (p<0.05). In the placebo group, OATT was decreased from 150.37±31.71 hours to 128.47±32.80 (p>0.05) and stool frequency was increased from 1.5110.39 to 2.37H.85 per weekwithout statistical significance (p>0.05). Laxative consumption decreased in the cisapride group when compared to placebo group. While those who used laxative were 2/17 (12%) (p<0.01) in the cisapride group, these were 15/17 (88%) (p>0.05) in the placebo group. It is concluded that cisapride decreases OATT and may improve bowel habits in patients with idiopathic chronic constipation and may reduce laxative consumption.