To evaluate in situ lymphocyte responses in cell-mediated immune tissue injury, we have developed an approach for propagation of human allospecific T lymphocytes directly from tissue biopsies. We have utilized renal allograft tissue obtained from eight patients undergoing cellular rejection. Needle biopsy tissue was cultured in medium containing interleukin 2 (IL 2), including recombinant-DNA-produced IL 2. In each case, lymphoblasts migrated out of the tissue and increased in numbers, especially adjacent to the tissue. In two cases in which there was no cellular infiltrate present in the biopsy, no lymphocytes proliferated in vitro. Instead, fibroblasts eventually filled the wells from these allograft biopsies. The continued presence of the allograft tissue enhanced the viability and growth of the lymphoblasts in cultures from rejecting allografts. The isolated lymphoblasts had surface markers of mature OKT3+ lymphocytes of either OKT4+ or OKT8+ subsets. OKT8+ cells predominated. There was variability (41 to 97%) in the percentage of T lymphoblasts that bore surface HLA-DR antigens. In assays of lymphoblasts obtained from eight separate renal allografts, there was donor-specific cytotoxicity, and in all but two of the cases there was donor-induced proliferation. The specificity of the cytotoxic reaction was tested by using 51Cr-labeled, PHA-stimulated target cells prepared from a panel of HLA-typed donors. Proliferation was tested after 48 hr in the presence of mitomycin C-treated peripheral blood mononuclear cells as stimulator cells by using only 10(4) responder T lymphoblasts. Of particular note was that the cytotoxicity of the isolated lymphoblasts showed specificity against both "private" HLA class I alloantigens (of the allograft donor) as well as "public" cross-reacting epitopes. This method permits the propagation and functional characterization of in vivo-activated T lymphoblasts that are obtained from the actual sites of immune-mediated injury. Preliminary studies of other tissues with diverse inflammatory processes indicate the possible widespread applicability of obtaining in vivo-activated lymphocytes.