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Objective: To study the immune tolerance induced by bone marrow cell transplantation combined with short-term use of cyclophosphamide after pancreatic transplantation in diabetic rats., Methods: Type I diabetes mellitus was induced in BN rats with streptozotocin (STZ) intraperitoneal injection at a single dose of 45 mg/kg. Pancreatic transplantations were performed with the SD rats as donors and the diabetic BN rats as recipients. Twenty BN rats with type I diabetes mellitus were randomly divided into four groups. The BN rats in Group I received pancreas transplantations only. The BN rats in Group II received intraperitoneal injection of 150 mg/kg cyclophosphamide on the first day after pancreas transplantations. The BN rats in Group 11 received injection of 2.0 x 10(8) donors' bone marrow cells via the portal vein during the pancreas transplantations. The BN rats in Group IV received injection 2.0 x 10(8) donors' bone marrow cells via the portal vein during the pancreas transplantations and an intraperitoneal injection of 150 mg/kg cyclophosphamide on the first day after pancreas transplantations. The blood glucose of the rats was measured after transplantations. The graft functional survival time (GFST) was recorded. Peripheral blood was obtained two weeks after the transplantations to prepare single cell suspension for detecting chimera formation rate and the level of Vbeta11+ T cell by flow cytometry., Results: The average GFST of group IV was (18 +/- 2.2) d, significantly longer than those of group I (7.8 +/- 1.2) d, group II (8.2 +/- 1.6) d, and group III (8.8 +/- l.4) d (P < 0.05). The rats in group IV had significant lower level of Vbeta11+ T cells (2.5 +/- 0.3)% than those in the other groups (P < 0.05). Donors' bone marrow-derived cells could be detected in the peripheral blood of diabetic rats in group IV, with a chimeric rate of (10.0 +/- 2.3)%. No donors' bone marrow-derived cells were detected in the rats in other groups., Conclusion: Bone marrow cell transplantation combined with short-term use of cyclophosphamide promote chimerism formation and induce immune tolerance in rats with pancreatic transplantations, which prolongs pancreatic graft functional survival time.