The effects of immunosuppression with cyclosporin A and prednisolone regimens for allogenous iliac crest bone grafts used for mandibular reconstruction were investigated in 40 miniature pigs, for periods of 2, 4 and 16 weeks. Autogenous and allogenous bone grafts without immunosuppression served as controls. Specimens were evaluated by routine histology, direct magnified radiography and fluorescence microradiography. Four out of five autogenous transplants showed a preserved vascular architecture and bony union. None of the allogenous transplants without immunosuppression survived. Primary bone healing of the allografts was noted after short-term immunosuppression. However, occlusion of the nutrient vessels was noted ten days postoperatively. The allografts were not rejected after cessation of the immunosuppressive therapy within an observation period of 4-12 weeks. Revascularization of all areas of the allografts and creeping substitution of the transplanted bone were noted after seven weeks. Infection of the allografts, with failure of bony union, was noted in nine animals, but primary healing of allografts with short-term immunosuppression was demonstrated.