Abstract: Quantitative and morphlogic studies of biologic effects of supranormal temperatures（42—44℃） and radiation on the gastric cancer cells （SGC-7901） were performed, using the cell and colony counts to disclose the effect of hyperthermia and radiation on the population and subpopulations of cells affected. The results showed that both hyperthermia （30 rain, at 43℃） and radiation （500 rad） exhibited cell killing effect and the growth curves changed downward, and a synergistic interaction of heat plus radiation was demonstrated when two were applied within 30 min. The concentrations of potassium ions in the media incressed with cell killing, and partial, transitory cell cycle redistribution occurred following, heating or radiation. A relatively marked division delay was observed following heat treatment, much more prominent. As compared to that following radiation. It seems to be reasonable to suggest that the synchronization effect may be used to hit the cycling tumour cells during their most radiosensitive phase.