SummaryCoagulation-time is the best way to watch the treatment with heparin. The best method seems to be that of Lee-White. Usual methods using capillary tubes or glass plates must he avoided. Prothrombine time cannot be used in control of patients treated with heparin.Such a control may be omitted when heparin is given intravenously every four hours ; When the drug is associated to some kind of solvant in order to delay its effect, the coagulation-time must be frequently checked, not to avoid over-dosage, but to warrant a sufficient administration of the drug.