The four loop (W) reservoir was developed with the aim of improving the functional results of the J reservoir and to avoid the need for catheterization often seen with the S reservoir. It is no more difficult to construct and results in better function. Sixty-four patients have undergone the procedure. There were no deaths. Mean hospital stay (including ileostomy closure) was 24 +/- 8 days. The reservoir has been removed in one patient (one week postoperatively) who was found to have a Dukes' B rectal carcinoma. Function has been assessed in 51 patients (mean follow-up 18.6 +/- 8.9 months). Frequency of defaecation per 24 h is 3.3 +/- 1.0 (range 1-8) with night evacuation in 14 per cent. Antidiarrhoeal medication is required by 20 per cent of patients. Continence is normal in 92 per cent, and 8 per cent have minor leakage. All patients defaecate spontaneously.