AbstractFollowing exposure of CHO‐K1 cells to137Cs irradiation at doses up to 20Gy, a delay in G2was observed to occur in cells permitted to divide normally, while cells induced to become giants by means of cytochalasin B demonstrated a minimal delay in the transition 2C–8C suggesting that the inhibition of cytokinesis results in modification of one or more cell cycle checkpoints. We postulate that this may occur as a consequence of damage tolerance, or by a feedback loop resulting from the reorganisation of the cytoskeleton that precludes cytokine