One must know tumor cell kinetics in order to devise a rational drug regimen for gliomas. With tritiated thymidine, the Labelling Index of astrocytomas is less than 1 per 100; of glioblastomas from 5-10 per 100. The duration of S phase is fairly constant, ranging from 7 to 10 hours. Double radioautography reveals a cell cycle time of 2 to 3 days and a Growth Fraction of 10 to 30 per 100 in glioblastomas. Calculations based on volume of tumor at recurrence after a gross total resection, analysis of primer dependent D.N.A. polymerase (P.D.P.), and analysis of cells by Flow Microfluorometer, all confirm these approximate figures. Thus most of the cells of a glioma are not sensitive to a cell-cycle phase specific drug. Such an agent, if given, should be administered over a 2 to 3 day period, in order to affect as many cells as possible. The most important part of a drug regimen should be an agent which attacks non-proliferating as well as proliferating cells, such as an alkylating agent. The effects of various drugs and schedules can be examined by animal models with the technqiue of colony forming efficiency.