Studies of the Mode of Action of ]Y-Isopropyl-o;-(2-methylhydrazino)-p-toluamide1

the drug occurred with the formation of one or more substances which was inhibitory to each of the 3 systems. The inhibitory action was approximately equally manifest against DNA and RNA synthesis. The inhibition of protein synthesis was delayed in onset and was likely a consequence of a diminished rate of nucleic acid synthesis. Evidence was obtained which indicated that the inhibitory component was not H202The inhibitory ac tion of MIH on DNA synthesis was not antagonized by nucleosides, DNA, or RNA, but was reversed upon washing the cells free of the drug; no binding to the cells could be demon strated. There was no degradation by the drug of pre-existing DNA. At concentrations which were inhibitory to nucleic acid synthesis, the rate of utilization of glucose was unaffected.