Conservation of the anal transition zone (ATZ) has been deemed necessary for continence after coloanal anastomosis (CAA) with reservoir. Therefore, we have studied functional and manometric results after CAA with reservoir and excision of the ATZ in 18 consecutive patients (mean age, 65.2 years; ten males and eight females), 17.4 months after closure of a temporary loop colostomy (Study 1). Twelve of the 18 initial patients were studied again 30.2 months after closure (Study 2). In Study 1, all patients underwent 1) a standardized interview, 2) a manometric study with measurement of anal pressure at rest (PR), voluntary contraction (VC), inhibitor anal reflex (IAR), conscious sensation (CS), and maximum tolerable volume (MTV), and 3) a liquid continence test (LCT) with measurement of colonic reservoir pressure during infusion. In Study 2, patients underwent all the same tests except the LCT. Results were compared with those of six controls (mean age, 65.8 years; two females and four males). In Study 1, 14/18 patients were continent; PR, VC, and CS did not differ among continent patients, incontinent patients, and controls. MTV was significantly lower in incontinent patients (mean +/- SD, 165 +/- 46.5 ml) than in continent patients and controls (mean +/- SD, 261 +/- 50.8 ml vs. 250.7 +/- 83 ml). IAR was not observed in continent or incontinent patients but was observed in controls. Contraction waves in the colonic reservoir during LCT were more frequent in incontinent patients (4/4) than in continent patients (4/14), and their amplitudes were higher (119 vs. 32 mm Hg). In Study 2, 12/12 patients were continent; PR and MTV remained unchanged except in the two initially incontinent patients, in whom MTV was increased. VC was slightly increased (94.7 vs. 116 mm Hg). IAR remained absent in all patients. We conclude that 1) excision of the ATZ did not increase the risk of incontinence, and 2) poor functional results were mainly due to small MTV and contraction waves in the colonic reservoir.