When patients die of pulmonary embolism following operation or childbirth, a feeling of helplessness and discouragement prevails until the incident is forgotten. Many months pass before the occurrence of the next one. It is remarkable, however, that the survey of large collective statistics reveals a fairly steady incidence in large services, namely from 0.1 to 0.2 per cent of all operations, 2 per cent of all deaths, 6 per cent of postoperative deaths and about 10 per cent of all autopsies. The prevention of postoperative or postpartum thromboses and the investigation of types of patients, types of diseases and types of operations which are especially endangered by pulmonary embolism are possible avenues of approach to the problem. In this discussion, however, we wish to limit ourselves to observations on the value of early diagnosis and the employment of simple procedures which may reduce its incidence and its high mortality. THE