One of the most important mechanisms to regulate DNA replication in eukaryotic cells is to regulate the initiation of the replication. Investigations into SV40(simian 40)and Saccharomyces cerevisiae systems provide instructive suggestions to the mechanisms of replication initiation in eukaryotic systems and maneuvers with which the initiation are concerted with cell cycle. Many functions of protein factors involved in initiation of replication in eukaryotic cells are being clarified. And the cycle-dependent regulatory pattern is gaining experimental supports. Two regulation points in cell cycle for DNA replication initiation and the roles played by cyclins are mainly introduced. The relationship between carcinogenesis and the disturbance of replication-cycle is also discussed at appropriate point, which hints at the significance of initiation regulation.