Lung homotransplantation was performed in 15 pairs of dog. Methotrexate and R.E.S. blocking were used to prolong the survival time. Details of handling the transplant, operative technique and management of the recipient were discussed and following results were obtained: 1]. 7 dogs out of 15 dogs of homotransplantation of lung were survived beyond 3 days. In the group of dogs treated with methotrexate, the average survival was 8.5 days, and in the group of dogs treated with R.E.S. blocking, the average survial was 9.7 days with longest survival of 17 days. 2]. The causes of immediate postoperative death in homotransplantation of dogs were lung edema and disruption of bronchial anastomosis. 3]. The main causes of death in successful homotransplantation dogs which were survived beyond 3 days were infection of lung parenchyma and bronchial necrosis rather than the occurence of graft rejection. 4]. Graft rejection was not revealed even after 7 days of operation in the group treated with methotrexate as well as in the group treated with R. E.S. blocking. This finding made it suggest that the R. E.S. blocking may be effective to control the rejection reaction. 5]. Even though the pulmonary function of transplanted lung was revealed the evidence of severe impairment immediate after operation by bronchospirometry, it was increased gradually and 10 days after operation the minute ventilation and oxygen uptake were decreased 8%, 13% respectively less than pre-operative one.[KTCS 1969;1:25-40]