We prospectively evaluated 38 adult patients with chronic constipation with and without defecatory difficulties using a newly described scintigraphic test to measure rectal emptying and compared them to 20 healthy controls. All patients underwent anorectal manometry, and 30 who complained of infrequent defecation underwent a colonic transit study using radiopaque markers. Control subjects promptly evacuated both 100 ml and 200 ml artificial stool in a characteristic fashion, but three evacuated none of the 100-ml volume and two had no evacuation of the 200-ml stool (inhibited controls). Constipated patients exhibited three patterns of emptying: (1) normal emptying of both volumes (47%); (2) poor emptying of both volumes or inhibited defecation (29%); and (3) normal emptying of the 200-ml but abnormal evacuation of the 100-ml volume (24%). An abnormal expulsion pattern during manometry occurred in 21% of patients and was strongly associated with the inhibited defecation pattern. However, defecation patterns could not be predicted on the basis of age, gender, symptoms, duration of complaints, colonic transit, or other rectal manometric parameters. Although rectal scintigraphy has potential advantages as a diagnostic test in terms of quantitation and decreased radiation exposure, the inability of the test to distinguish patients with slow transit constipation and defecatory complaints makes the potential utility of this test of uncertain value in clinical and investigative settings.