The major step toward successful tracheal transplantation is revascularization of the grafted trachea. There are many reports that although omentopexy is an effective method to facilitate neo-vascularization in tracheal transplantations, the procedure has not been accepted universally in the transplantation field. It remains unclear whether an omentopexy can successfully revascularize tracheal graft regardless of the length of graft. This study was undertaken to assess the usefulness of omentopexy for long-segment(more than 4 cm) tracheal allotransplantation. We have performed six tracheal transplantations with omentopexy (group A) and four tracheal transplantations without omentopexy (group B) in mongrel dogs from July 1993 to February 1995. Five mid-portion tracheal rings were removed from ten donor dogs and ten corresponding tracheal rings were removed from the ten recipient dogs. The excised tracheal rings from the donors were transplanted to the recipient tracheal-excised sites. All the recipients were given cyclosporine, azathioprine, and prednisolone for immunosuppression in the post-operative period. The histologic results of all the surviving members of group B were better than those of the group A. These findings indicate that omentopexy has a limitation, it is not a major method for graft revascularization. Therefore the length of the tracheal graft was greater than 4.0 cm, for its viability, a longer tracheal graft requires some other blood supply aside from the omentopexy.