Addition of IL-4 (1,000 U/ml) to either high or low concentrations of IL-2 augmented tumor-infiltrating lymphocytes (TIL) growth from human melanoma. Weekly restimulation with irradiated tumor cells in conjunction with IL-4 allowed enhanced growth of TIL. With low-dose IL-2 (10 U/ml) and IL-4, expanded TIL had little cytolytic activity against Daudi or allogeneic tumors. Further, IL-4 augmented the total lytic activity against autologous tumors in most cases. With high-dose IL-2 (1,000 U/ml), IL-4 addition decreased nonspecific killing activity against Daudi or allogeneic melanomas in many cases, and reciprocally augmented cytolytic activity against the autologous melanoma in many cases. This suggests the possible use of IL-4 in cancer therapy, especially in adoptive cellular immunotherapy using TIL or in conjunction with IL-2 administration.