鈥� The effects of imipramine hydrochloride on cell proliferation were investigated in leukocyte cultures derived from normal volunteers. Nine different doses of imipramine were added in vitro at random for 4, 24, 48, and 68 hours, the three lowest concentrations being within the range of plasma levels reported in psychiatric patients receiving the drug therapeutically. Cell proliferations, as measured by mitotic index, was affected by both the concentration and the duration of drug exposure; the higher the dose and/or the longer the drug in culture, the lower the mitotic index. lmipramine concentrations corresponding to therapeutic plasma levels had no effect on mitotic index regardless of the length of exposure.