To determine whether a persistent contraction of the pelvic floor muscle during straining, as observed in constipated patients during defaecography, was due to a conscious action of the patients or really represented a functional disorder, segmental colonic transit studies were performed in 24 patients in whom the diagnosis spastic pelvic floor syndrome was made. Abnormal segmental transit indicating outlet obstruction occurred in 92% of the patients. Four different types of segmental transit abnormalities were observed which suggested that the spastic pelvic floor syndrome involved a functional outlet obstruction leading to retrograde filling of the colon and severe straining. A causative relation with other anorectal abnormalities is suggested.