The major thrust of this research project continues to be the molecular pharmacology of the cell cycle involving the study of agents which are known to interfere with DNA synthesis and have useful or potentially useful clinical applications. In this grant year, increasing emphasis will be placed on the study of combinations utilizing synchronized hamster fibrosarcoma cell line derived by transformation with ara-C. More emphasis will be placed on relating these studies to pharmacokinetic measurements of the same drugs in man and developing models using isolated nuclei.