The indicated cell lines, in log-phase growth, were exposed for 16 hours to ADR (0.125 μmol/L), CDDP (1 μmol/L), CPT (0.125 μmol/L), N-Mus (0.1 μmol/L), Taxol (0.5 μmol/L), or VP16 (0.1 μmol/L). Nuclei were then stained with propidium iodide, and their cell cycle distribution determined by fluorescence-activated cell sorting as previously described.18 Preliminary experiments indicated that the distributions shown were reached by 12 hours after drug exposure and did not change significantly before the onset of detectable apoptosis. None of the conditions used here induced more than 5% to 10% apoptosis as determined by the presence of subdiploid nuclear populations and trypan blue staining.