Eukaryotic DNA replication is confined to a specific portion of the cell cycle (the S phase) and is highly regulated: every segment of the genome is replicated once per S phase, but no segment is normally replicated more than once. How this tight control of replication is accomplished is not known. However, the pace of research into the mechanisms of eukaryotic DNA replication and of cell cycle control has accelerated dramatically within the past few years. Recent investigations provide, for the first time, hints of how control of replication may be coupled at the molecular level to control of the cell cycle. This review is intended to bring these recent investigations to the reader's attention and to speculate about their relationships to each other.(ABSTRACT TRUNCATED AT 250 WORDS)