INTRODUCTION: Amitriptyline, a tricyclic antidepressant agent with anticholinergic and serotoninergic properties, has been used empirically in the treatment of idiopathic fecal incontinence with good results. METHODS: An open study was conducted to test the response to amitriptyline 20 mg daily for four weeks by 18 patients (2 males) of median age 66 years with idiopathic fecal incontinence. Incontinence scores, number of bowel movements, computerized ambulatory anorectal pressures, and pudendal nerve terminal motor latencies were evaluated before and after four weeks of therapy. Twenty-four control subjects (10 males) of median age 61 years were also assessed. RESULTS: Amitriptyline improved incontinence scores (median pretreatment score=16vs. median posttreatment score=3;P<0.001) and reduced the number of bowel movements per day (P<0.001). Amitriptyline also decreased the frequency (median pretreatment frequency=4.5 per hourvs. median immediate posttreatment frequency=1.2 per hour (P<0.05); control median frequency=0.3 per hour) and the amplitude of rectal motor complexes (median pretreatment rectal pressure=94 cm H₂Ovs. median immediate posttreatment rectal pressure=58 cm H₂O (P<0.05); control median rectal pressure=36 cm H₂O) and improved anal pressures during these events (P<0.001). CONCLUSIONS: Amitriptyline improved symptoms in 89 percent of patients with fecal incontinence. The data support that the major change with amitriptyline is a decrease in the amplitude and frequency of rectal motor complexes. The second conclusion is that drug increases colonic transit time and leads to the formation of a firmer stool that is passed less frequently. These in combination may be the source of the improvement in continence.