Some experimental studies on skin homograft were performed between A and C 57 BL or Db strain of mice, to investigate the influence of qualitative and quantitative difference of graft antigen upon homograft rejection reaction. In this study, difference in amount of graft antigen in homograft rejection was tested in the experiment with two kinds of different size of normal skin (1.0cm.×2.0cm. and 2.0cm×4.5cm.). The normal skin was kept frozen either simply or in 15 % glycerin in saline for 3 to 24 hours to have physical denaturation of the graft, and to have a biologically deteriorated graft, atrophied skin was harvested from mice, which were administered with 1 mg. of prednisolone intraperitoneally daily for 3 to 9 weeks. The results obtained were as follows, 1) The larger piece of skin survived longer than the smaller piece, although no significant difference in time before onset of rejection was observed. The rejection of the second set graft was accerelated, regardlessly of the size of the first graft. This suggested that the longer survival of the larger graft was due merely to requirement of excess time to complete the rejection process after its onset. 2) There was no significant difference in the survival time of the first graft between the frozen and normal skin, and the same was also observed between the grafts which were simply frozen and were frozen in 15 % glycerine in saline. No second set phenomenon was observed when the skin simply frozen for 3 to 24 hours was used as the first graft. However, the accerelation rejection of the second set graft was clearly observed in mice who received the first graft which was kept frozen in 15 % glycerine saline for 3 to 6 hours. This indicated that freezing storage of skin in 15 % glycerine saline for up to 6 hours could saved enough antigen of the skin to sensitize the mice for the second set phenomenon with its first graft. 3) The atrophied skin obtained from prednisolone-treated mice survived longer than the healthy skin from untreated mice in its first graft. When the second set graft was made on mice who received and rejected the skin from prednisolone-treated mice, the rejection was accerelated as equally as in mice who received and rejected the normal skin as first graft, indicating that in skin showing simple atrophy, though it was macroscopically and histologically demonstrable, no qualitative deterioration of transplantation antigen might occur, in contrast to the occurrence of quantitative reduction of the antigen according to the grade of atrophy. 4) The results were also obtained from the study in the analysis of the serum γ-globulin and tissue amino acid in the skin, to support the above statements.