The hazard of hemorrhagic diatheses resulting from the use of dicumarol® has been repeatedly emphasized, and considerable accumulated clinical experience has established definite contraindications to its prescription. As outlined by Barker1and Allen,2the conditions under which the drug should be used cautiously, if at all, include significant hepatic and renal insufficiency, ulcerative lesions of the gastrointestinal tract, purpura of any type, blood dyscrasias with a bleeding tendency and, particularly, thrombocytopenia, subacute bacterial endocarditis and after recent operations on the brain or spinal cord where even minor degrees of bleeding might be associated with grave consequences. To this list others3have added severe hypertension, recent threatened abortions and obstetric cases near term. Lack of adequate and reliable laboratory facilities for the daily measurement of prothrombin activity must be regarded as the most important of all contraindications. The official Swedish civil and army medical committee have concluded that