Many attempts have been made to prolong the survival of homografts by suppressing the reticuloendothelial system of the host with drugs and other agents. A study of the Bagg lymphosarcoma in our laboratory showed that the growth of homografts of this tumor in rats was enhanced when the recipient animals were preconditioned with certain cytotoxic drugs and antimetabolites.4 This study has been extended to determine if these agents affect the survival of homograft of normal skin. The transparent chamber technique was used because it provides an accurate criteria of survival of homografts. Skin is an organ which is very sensitive to the homograft rejection mechanism. Drugs which affect the survival of homografts of skin might have a similar effect upon homografts of other tissues. It is hoped that the simple technique described in this paper might be useful in the selection of drugs for the conditioning of animals for