Skin homografting was performed on the dorsum of the left ear of adult rabbits, and the effects of cortisone and cyclophosphamide on the response of the regional lymph node were studied. The main results are briefly summarized as follows:
1) In the rabbits that received daily injections of 10 mg of cortisone, skin homograft survival was prolonged to 25.6±4.73 days, and in those treated by daily injections of 25 mg of cyclophosphamide per kilogramm of body weight to 19.5±2.02 days, as compared with the average survival time of 9.5±0.28 days in controls. With 12.5 mg of cyclophosphamide per kilogramm of body weight, only a little prolongation of skin homograft survival was observed.
2) Increase in the percentage of weight of the regional lymph node, as compared with that of contralateral node, was much lower in the cases with healthy grafts than in the cases with rejected grafts. The longer was the skin homograft survival, the greater this dlfference.
3) Even when the skin homograft survival was markedly prolonged, a slight degree of proliferative response of the regional lymph node was clearly recognized, and this is considered to be a nonspecific proliferative response of lymph node in transplantation immunity.