Maximal anal pressures have been measured after proctoscopy in 145 patients with hemorrhoids, 48 patients with anal fissure, and 78 asymptomatic control subjects. Anal pressures in patients with hemorrhoids (106 +/- 40 cm H2O) and anal fissure (130 +/- 43 cm H2O) were very significantly higher than those of controls (88 +/- 34 cm H2O) (P less than 0.001). Because patients with anal fissure have high anal pressures, these patients should benefit from manual dilatation of the anus or lateral subcutaneous sphincterotomy; however, only young male patients with hemorrhoids have anal pressures that are significantly higher than age- and sex-matched controls. Digital assessment and the two finger test are unreliable indicators of high anal pressure. These results indicate that measurement of anal pressure is useful in assessing the suitability of manual dilatation or sphincterotomy in the treatment of hemorrhoids.