The two step small-bowel transplantation was performed experimentally in pigs. Both ends of heterotopic segmental allografts of 100 cm small bowel were enterostomized during the first operation. After 4-6 weeks, the allograft was interposed in the continuity of the intestine. Rejection was developed in Group I (n = 6) without immunosuppression. The mean survival time of the grafts was 17.7 +/- 7.6 days, and recipients were alive after resection of necrotic grafts. The animals of Group II (n = 6) were treated by cyclosporine concomitantly with azathioprine and methylprednisolone. Two pigs were killed for severe pneumonia on day 92, 97 and the grafts were alive, the other four recipients and their grafts survived for more than 300 days, 270 days, 260 days and 260 days respectively. No GVHD was observed and rejection was the major problem in segmental intestinal transplantation.