The DPN contents of fast growing tissues like testicle and gut show a significant decrease 24, 48, and 96 hrs after administration of cytostatic agents; at the same time there is a back-up of TP and FDP, two compounds known as intermediaries in glycolysis. However, there is no decrease of DPN in tumor tissue nor is there any back-up of the intermediaries under similar conditions. The mode of action of Methylhydrazine appears to differ from other cytostatic agents.