76 patients with diarrhoea due to a variety of causes and seen consecutively in the gastrointestinal clinic were questioned about the frequency of faecal incontinence. 51% (39) of these patients had incontinence but of these fewer than half (19) volunteered the information spontaneously. Only 4 patients provided clear evidence of a possible predisposing cause. Anal-sphincter pressures, particularly the maximum squeeze pressures, were significantly lower than normal in the incontinent patients, and their ability to retain saline infused into the rectum was significantly impaired. All but 7 of 42 continent subjects could retain more than 500 ml before leaking, whereas 19 of 22 frequently incontinent subjects leaked after infusion of less than 500 ml. These results suggest that incontinence is a common but frequently unvoiced symptom in patients with diarrhoea. It should be actively sought since it may be the prime reason for the patient to seek help with a complaint of "diarrhoea". The saline-infusion test is a simple method of measuring this disturbance of anorectal function.