Cells respond to a variety of signals by activation of a phospholipase C which catalyzes the phosphodiesteric cleavage of phosphatidylinositol 4,5bisphosphate to generate intracellular second messengers, inositol 1,4,5-trisphosphate and 1,2diacylglycerol. Previously, we described the isolation of an inhibitor for inositol-specific phospholipase C from Actinomadura sp. This inhibitor therefore may be a valuable tool for elucidating the mechanism of the signal transduction pathway of various systems as well as a hopeful candidate for cancer chemotherapy1'2). On the other hand, diacylglycerol kinase phosphorylates diacylglycerol to form phosphatidic acid. This enzyme is known to be elevated by extracellular stimuli to accumulate phosphatidic acid by phosphorylating diacylglycerol, and to be involved in the attenuation of protein kinase C by decreasing the concentration of diacylglycerol in the cells3). However, the detailed function of this enzyme remains to be clarified. Thus, an inhibitor of diacylglycerol kinase would be a useful reagent to explore the role of this enzyme in the signal transduction pathways in various systems and a possible candidate for cancer chemotherapy. This report describes the isolation of D2597 substances from Drechslera sacchari, which are inhibitors of diacylglycerol kinase from bovine thymus.