In a prospective electromyographic and manometric study on 23 women (average age 52 years) with obstructive defecation disorder the activity of the external anal sphincter muscle and the puborectal muscle was investigated at rest and during contraction and straining. The control group consisted of 22 healthy women with an average age of 53 years. The main aim of the study was to investigate the functioning of the two muscles during simulated defecation (maximum strain) and to examine any changes in the pressure ratio in the rectum and the anal canal during this stimulation. There were no significant differences in the resting pressure, the contraction pressure and the straining pressure (in the rectum and the anal canal) between the two groups. The functioning of the puborectal muscle and the external anal sphincter muscle was largely the same in both the study group and the control group. No statistically significant differences were found between the two groups except in the amplitude of contraction. When we tried to list the change in the activity of the muscle as an index of anism, we were not able to objectify such a change for either the external anal sphincter muscle or the puborectal muscle. We therefore conclude that the increase in the activity of the voluntary muscle of the pelvic floor observed on electromyography during defecation does not indicate a pathologic condition but is a functional state.