The single most significant conclusion to emerge from examination of the current status of deep vein thrombophlebitis is the rapidly increasing incidence of the disease. One's first reaction to this observation is that certainly an increasing awareness of the disease must be largely responsible for an apparent overall increase in its incidence. But closer study raises strong suspicion that the finding is not only apparent; it may be real. Evidence for this deduction cannot be drawn from a simple mathematical tabulation of reported cases. The protean nature of the disease, inconsistent record-keeping, incomplete reporting, and the vagaries of diagnosis make it necessary for meaningful information to be derived from a broad body of evidence which includes studies of sequelae, such as pulmonary embolism and postphlebitic syndrome; from laboratory data which reveal the effects of various drugs on physiologic responses of the vascular system and on coagulation properties of the blood;