Delayed-type hypersensitivity (DTH) response is generally considered as one of major mechanism of anti-tumor immunity in vivo. We studied the effect of radiation on the immune spleen cells mediating tumor-specific DTH response based on an local adoptive transfer system. The spleen cells from C3H mice which were immunized with syngenic MH134 hepatoma cells were employed for the effector cells. The immune spleen cells were irradiated in vitro. Then the spleen cells and mitomycin C (MMC)-treated MH134 cells were mixed and inoculated into the hind footpad of normal C3H mice. Twenty-four hours later, the thickness of the footpad was measured with micrometer and increase in the footpad thickness was calculated comparing with a value before the inoculation. Irradiation with 4 Gy-12 Gy did not affect the DTH response. Then irradiation over 16 Gy dose dependently decreased the DTH response. Irradiation with 20 Gy decreased the DTH response about 50% and 28 Gy abolished the response to a control level. As two types of cells, antigen specific effector T cells and non-specific effector cells such as macrophages, are required to induce DTH response, we studied which type of cells is suppressed by irradiation. Non-irradiated normal spleen cells as a source of non-specific effector cells were added into the irradiated immune spleen cells. The addition of normal spleen cells to 20 Gy irradiated immune spleen cells recovered the DTH response to a control level of non-irradiated group. The other hand, the addition of normal spleen cells to 32 Gy irradiated immune spleen cells failed to recover the DTH response.(ABSTRACT TRUNCATED AT 250 WORDS)