Previous studies in our laboratory have demonstrated the existence in normal cells of kinase-mediated control mechanisms that are apparently lost during neoplastic transformation. Specifically, staurosporine, a general kinase inhibitor, at concentrations of 1-10 ng/ml arrests normal cells in G1 but has no effect on the progression of transformed cells through the G1 phase. High levels of the drug (50-75ng/ml) arrest both normal and transformed cells in G2 phase. We have undertaken a series of studies involving cell cycle analysis and BrdU incorporation during S phase to determine if there are other differential effects of staurosporine at other phases of the cell cycle. Presently we are studying the effects of the drug on the temporal arrest point in G1 and G2 in both normal and transformed cells to determine the time at which the block occurs. It is an important aim to determine the role of the kinases inhibited by staurosporine on the progression of cells through all phases of the cell cycle.