Heparin and dicumarol are both useful drugs but each has its limitations and accordingly search goes on for newer drugs that lack some of these limitations. A new anticoagulant, phenylindandione produces a prothrombopenia more rapidly than dicumarol and its catabolism is equally more rapid. This, therefore, aroused interest in clinical trials utilizing this new prothrombopenic agent. The drug is a light yellow, crystalline compound put up in tablet form and administered by mouth.