A combined electromyographic and cineradiologic investigation in patients with defecation disorders. Records from 20 patients on whom defecography and electromyography were performed simultaneously because of defecation disorders were analyzed. According to the electromyographic investigation, the patients could be divided into three main groups: 1) normal sphincter reaction; 2) paradoxical sphincter reaction; and 3) combined reaction. Group A was characterized by a marked reduction of muscular activity during emptying and a pronounced closing reflex after emptying. This was followed by return of normal tonic activity. Patients in group B had no relaxation of the sphincters during emptying but a pronounced increased activity in the external sphincter and the puborectalis muscle. They also had severe emptying difficulties at defecography. No closing reflex was seen. In group C the electrical activity in the sphincters increased during moderate straining and when emptying was complete a clear closing reflex was seen. In this study, a dynamic visualization of the defecation together with a registration of electromyographic activity in the striated anal sphincters was performed. It was shown that patients with paradoxical sphincter reaction were lacking a closing reflex after emptying was complete. This has not been reported previously and is important evidence for the paradoxical defecation pattern. It was also shown that the patients with rectoceles had paradoxical sphincter reaction. 