OBJECTIVE: To calculate the colonic transit time (CTT) and to evaluate the effect of combined therapy of cisapride and lactulose on neurogenic bowel dysfunction in patients with chronic spinal cord injury. METHOD: This study was prospectively designed. Right (rCTT), left (lCTT), rectosigmoid (rsCTT), and total (tCTT) colonic transit times were measured using the radio-opaque marker technique in twenty patients with spinal cord injury (SCI group), of which mean age was 39 years (range: 13~67 years) and median duration after SCI was 15 months (4-252 months). Ten ambulatory stroke patients (mean age 49 years, median duration, 12 months) were also evaluated as control group. All CTTs in both groups were compared by unpaired Student's t-test. In SCI group, the therapeutic effect of combined administration of cisapride (10 mg p.o. t.i.d) and lactulose (134.0 g/100 ml, 30-45 ml per day p.o.) was statistically analyzed by paired Student's t-test. RESULTS: Total (p<0.0001) and segmental CTT (p<0.01) except right colon were significantly delayed in SCI group when compared to the control group. In SCI group, tCTT of non-ambulatory patients (n=13) and rCTT, lCTT, rsCTT and total CTT of ambulatory patients (n=7) were significantly decreased after the combined drug therapy (p<0.05). In ambulatory SCI patients, duration after injury showed negative correlation with tCTT (Pearson's correlation coefficient r = 0.8407, p=0.0178). CONCLUSION: Combined therapy of cisapride and lactulose can improve tCTT in SCI patients with neurogenic bowel dysfunction.