TIL were cultured from human renal-cell carcinoma (RCC) in 1,000 U/ml rIL2 and restimulated with autologous tumor in efforts to establish which conditions would best expand the number of lymphocytes cytotoxic for autologous tumor. Greater cell yields resulted from multiple restimulations of TIL with autologous tumor. In most instances, these TIL lysed autologous tumor better than TIL grown in rIL2 alone. Enhanced proliferation was seen also after restimulation of TIL with allogeneic RCC as well as with tumor cells of non-renal origin. Although in some instances lysis of autologous tumor appeared to be specific, restimulation with autologous tumor did not consistently result in the generation of specific cytolytic T cells. Attempts to culture more specific cytolytic T cells by using 50 U/ml rIL2 were successful in expanding TIL with enhanced lytic activity; however, this activity was not specific for autologous tumor. The phenotype of the tumor-restimulated TIL generally did not change. In most of the TIL cultures, CD3+CD4+ cells were predominant with low numbers of CD3+Leu19+ cells and minimal numbers of CD3-Leu19+ cells. Thus, the cytotoxic response to tumor was mediated by T cells and not NK cells. Overall, our data indicate that restimulation of TIL with autologous tumor may be beneficial for growing larger numbers of cells which have increased lytic activity and for prolonging the presence of lytic activity among the expanded TIL.