We did 97 limb homografts among histoincompatible rats, Wistar and Fischer 344 pairs, and we concluded as follows. 1. Using microvascular anastomoses, rats are technically, immunologically, and economically superior to other animals for the study of limb homografts. 2. The homografted legs in animals without the use of any immunosuppressive agents were rejected by the 14th postoperative day (average, 12.5 days) among the Wistar and Fischer 344 pairs. The common features of limb rejection became clear, both macroscopically and histologically. 3. Rats immunosuppressed with azathioprine and prednisolone retained the homografted legs intact for 24, 21, and 17 days (when the recipient rat died). Other immunosuppressive drugs (6-MP, prednisolone) did not delay rejection.