Numerous factors have recently been identified that are involved in the control of cell cycle checkpoints. It was found that the DNA damage-induced G1 and G2 delays are associated with a regulatory system consisting of cyclin-dependent protein kinases (CDKs) associated with cell cycle phase specific cyclins. This article reviews the recently discovered associations between cell cycle regulation and cell death or recovery in the in vitro cellular systems exposed to ionizing radiation. The concept of alarm signal is explained. A brief comment on the role of apoptosis in the postirradiation cell fate is included.