A unique method for assessing the in vivo recovery of cellular immunity following sublethal irradiation and syngeneic bone marrow transplantation of CBA/J mice is described. This method employs the serial surgical implantation of a urethane sponge matrix followed by impregnation of the sponge matrix with alloantigen. Sponge matrices were harvested from each mouse subject at 2 weeks, 4 weeks, and 8 weeks post transplant with and without treatment with interleukin-2. Recovery of cellular immunity was assessed as a function of cytotoxic T lymphocyte activity via cell-mediated lympholysis using chromium labeled targets. Repetitive procedures of implantation and removal of the matrices from the same animal were surgically feasible and were exceptionally well tolerated by the animals with insignificant morbidity thereby permitting continuous monitoring of immunologic recovery. Although the results of treatment with interleukin-2 were inconclusive, this method provides a sensitive, technically manageable means by which to assess an antigenic response in vivo at predetermined time intervals utilizing the same mouse subject. The method additionally affords the potential of being applicable to the in vivo assessment and manipulation of other aspects of the immune response.