Rectosigmoid motility, anal manometry, and radiopaque marker studies have suggested the presence of several patterns of altered colonic transit in patients with chronic idiopathic constipation. Colonic transit scintigraphy was used to evaluate 23 constipated patients. After oral passage of a tube to the cecum, 50 microCi of 111In-diethylenetriaminepentaaceticacid (111In-DTPA) were instilled, and abdominal images were obtained for 48 h with a gamma camera. The 95% confidence limit for the geometric center in normals at 24 h was used as a criterion to differentiate patients with colonic inertia from those with functional rectosigmoid obstruction. In patients with functional rectosigmoid obstruction, colonic transit was essentially normal. In colonic inertia, transit was delayed in the cecum and ascending colon, hepatic flexure, and transverse colon. These two distinct patterns of colonic transit may have different pathogenetic and therapeutic implications.