The most important component of continence is considered to be the puborectalis muscle which is reputed to function by creating a flap-valve mechanism in which the anterior rectal wall occludes the upper and canal. To elucidate this, anal and rectal pressures were measured simultaneously together with external anal sphincter and puborectalis electromyogram and synchronously superimposed on an image intensifier displaying the rectum outlined by barium. We studied 13 subjects at rest, and during a Valsalva manoeuvre. There was a significant rise in rectal and sphincter pressures (P less than 0.005) and external sphincter and puborectalis EMG (P less than 0.005). In a further 13 patients Valsalva manoeuvres were performed during proctography alone. In all subjects the anterior rectal wall was always clearly separated from the upper sphincter despite a maximal effort and a rectum filled with sufficient liquid to produce a desire to defaecate. These findings question the flap-valve theory of continence and suggest the puborectalis functions by sphincteric occlusion of the anal canal.