To solve frequently encountered clinical problems in the anorectal area, we have developed a simplified dynamic method of defecography. A radiopaque substance, the consistency of normal stools, is introduced into the rectum and the patient is then seated on a specially designed seat composed of superposed air chambers which, for technical reasons, are filled with water. The movements induced by evacuation of the rectum are recorded using 100-mm ampliphotography. After recording findings in 56 normal patients, we are able to define 5 criteria for "normal": increase in anorectal angulation, obliteration of the impression of the puborectal muscle, wide opening of the anal canal, total evacuation of the rectal contents, and normal resistance of the pelvic floor. The mean value of the anorectal angle (ARA) was 91.96 degrees (+/- 1.52 SEM) at rest and 136.76 degrees (+/- 1.51 SEM) during straining. The increase of ARA during straining is 44.8 degrees.