The antibody secreting B lymphocyte hybridoma cells were irradiated with ,60,Co γ-rays. A markedly dose-related depression of total production of specific antibody was observed. However, production of specific antibody per clone was raised with increase of radiation dose. The increase in antibody secretion by B lymphocyte hybridoma cells was lost after long term culture and freezing of survival cells. γ-radiation could induce potentially lethal damage of monoclonal antibody secreting cells, but this damage didn't affect the antibody secreting function of those surviving cells. These results indicate that ionizing radiation stimulates the secreting function of B lymphocyte hybridoma cells in the initial period after exposure.