The aim of this study was to compare segmental grafts of jejunum and ileum in a dog model. 14 segmental grafts, 8 ileal (Il. A) and 6 jejunal (Jej. A.), were successfully allografted as 120 cm-Thiry-Vella segments. Immunosuppressive therapy consisted of cyclosporin 25 mg/kg/day per os. Monitoring was performed by histology and absorption (maltose and xylose) studies as well as analysis of brush border enzymes. No cases of Graft-versus-host disease were observed. Six allografts (42.5 per cent) including 3 Jej. A. (50 per cent) and 3 Il. A. (37.5 per cent) were rejected during the first three months. Eight allografts (5 Il. A. and 3 Jej. A.) were tolerated for up to 3 months and were removed: 2 Il. A. and 2 Jej. A. were normal, while 2 Il. A. and one Jej. A presented with signs of chronic rejection and one Il. A. with advanced rejection. Jej. A. and Il. A. showed a similar course, by means of immunologic reactions as well as functional characteristics. It is concluded that there is no major difference between Jej. A. and Il. A. in the dog. Because of the specialized absorptive functions of the ileum and its adaptative properties, ileal segmental grafts should be preferred to jejunal grafts for the treatment of short-gut syndrome.