The aim of this study was to develop a method by which rectal and colonic activity could be examined during defaecation under physiological conditions, in order to evaluate whether the colon plays a role in defaecation. Subjects presented to the Nuclear Medicine department on the day following ingestion of oral In-111 labelled DTPA, when they developed the normal urge to defaecate. Defaecation took place in a private room while dynamic scintigraphy of the rectum and colon was recorded. Fourteen subjects were studied (8 normal subjects, 4 with constipation, 2 with irritable bowel syndrome). In 13 subjects the left colon was visualized during defaecation and emptying was clearly observed in 12. The right colon was visualised in 11 subjects and emptying was seen in 7. Mean percentage segmental evacuation was right colon 20%, left colon 32% and rectum 66%. Colonic emptying occurs during defaecation, which is not a process of rectal evacuation only. This has implications for the understanding of the pathophysiology of obstructed defaecation.