Physiological abnormalities in the anorectum of 34 patients with pruritus ani, and 20 age and sex matched controls were assessed. A saline infusion (1500 ml) test showed that leakage started after infusion of 600 ml in patients with pruritus ani compared with 1300 ml in controls (median values: P less than 0.001). There was an inverse relationship between the severity of the symptoms of pruritus ani and the volume of first leakage on the saline infusion test P less than 0.02. Studies to assess anal sphincter function, rectal sensation to balloon distension, rectal compliance, and perineal descent did not show any significant differences between pruritic patients and controls. However, pruritic patients without co-existing anal pathology had a significantly greater fall of anal pressure when a rectal balloon was inflated (57 per cent) when compared with controls (40 per cent) P less than 0.05.