The hypothesis that haemorrhoids result from chronic constipation was investigated by studying bowel habit, anal pressure profiles and anal compliance in 13 men and 10 women with prolapsing haemorrhoids, 12 women with severe constipation and 14 male and 11 female control subjects. Defaecation was less frequent in women than in men (P less than 0.01) but was independent of the presence of haemorrhoids. Patients with haemorrhoids and control subjects reported similar stool consistency and rarely admitted to straining. Severely constipated women complained of infrequent defaecation, straining at stool and hard motions, but none had prolapsing haemorrhoids. Haemorrhoids were associated with significantly longer anal high-pressure zones and significantly greater maximum resting pressures at all levels of anal distension (P less than 0.01), but minimum residual pressure during rectal distension and maximum squeeze pressure were not significantly different from control subjects. Maximum resting pressure was increased in patients of both sexes with haemorrhoids, but this reached statistical significance only in men (P less than 0.001). Constipated women had normal anal pressure profiles and maximum anal pressures. These data show that patients with haemorrhoids are not necessarily constipated but tend to have abnormal anal pressure profiles and anal compliance. Chronically constipated women do not necessarily have haemorrhoids but have normal anal pressure profiles and compliance. This casts doubt upon the hypothesis that haemorrhoids are caused by constipation.