Severe constipation often follows spinal cord injury. The aim of this study was to evaluate transit of contents through the large bowel in patients with paraplegia after a complete transverse lesion of the spinal cord. Transit through the right colon, left colon, and rectum was evaluated in 11 patients (eight males, 3 females; 17 to 63 years old) and data were compared with that of 37 healthy control subjects. In all patients there was either no, or abnormally low, transit at the level of the left colon and rectum. A minor degree of transit delay at the level of the right colon was also present in eight patients. These data indicate that constipation in patients with paraplegia is due to abnormal transit, mainly at the level of the left colon and rectum, and transection of the spine between the C-4 and T-12 vertebral levels causes alteration of large-bowel motor activity mainly at the level of the segments innervated by the parasympathetic fibers of the sacral outflow.