The symptoms of bypass enteritis are disabling sequelae in many patients after jejunoileal bypass. This is a preliminary report of efforts to devise a valve to prevent reflux into the bypassed intestine after jejunoileal bypass. Valve I (42 cases) was formed by dividing the ileum, everting the proximal end as one matures an ileostomy, and inserting this into the distal ileum. Only 12 of these valves were competent. Valve II (six cases) was formed by dividing the ileum and merely inserting the proximal bowel into the distal, allowing it to evert spontaneously as with an unmatured ileostomy. In two cases the valve was competent, but four cases became obstructed and this valve is mentioned only to be condemned. Valve III (19 cases) is similar to an isoperistaltic Kock valve, except that the intussuscepted ileum is first divested of its mesentery. All such valves have been competent. All 33 patients with a competent valve have been free of the stigmata of bypass enteritis, whereas 54% of 156 patients showed the symptoms of enteritis after conventional jejunoileal bypass. Images Fig. 1. Figs. 2a-c. Fig. 2b. Fig. 2c. Fig. 6.