Clinical and physiological study of anal sphincter and ileal J pouch before preileostomy closure and 6 and 12 months after closure of loop ileostomy. Spontaneous evolution of pouch and anal function, and absorption features has been assessed in 15 patients who underwent proctocolectomy with J ileal pouch anastomosis without conservation of a rectal muscular cuff. All the patients were studied before preileostomy closure and six and 12 months after the closure of the protection loop ileostomy. Stool frequency was identical at six and 12 months (mean +/- SEM: 5.0 +/- 0.4 and 5.3 +/- 0.5/day, respectively). Sixty-six percent of patients at six months and 40% of patients at 12 months need to defecate at least one time during night. Stool weight as well as steatorrhea decreased significantly six months after the closure of loop ileostomy (P less than 0.05). Mean resting anal pressure remained unchanged six and 12 months after closure of the loop ileostomy (41 +/- 6 and 45 +/- 5 cm H2O, respectively). Maximum squeeze anal pressures increased significantly at six (P less than 0.05) and 12 months (P less than 0.05). The rectoanal inhibitory reflex was always absent at the same period. The maximum pouch capacity increased significantly during the first six months (P less than 0.01) from 142 +/- 17 to 279 +/- 27 ml. The maximum infused volume during a saline continence test was not significantly different at six and 12 months; the percentage of evacuation of the reservoir and the volume at which the first ileal contraction appeared in the reservoir increased significantly (P less than 0.05) at six and 12 months. In conclusion, in patients with ileoanal anastomosis and pouch reservoir, the closure of the loop ileostomy is associated with spontaneous modifications of the anal and pouch parameters. 