The statement that amniotic fluid embolism is the most dangerous and untreatable condition in obstetrics appears to be true. It must be suspected in any patient who collapses or bleeds excessively during labour or the immediate post-partum period. Attempts should be made to secure a definitive diagnosis in life by examination of blood obtained from the right side of the heart and the sputum for elements of amniotic fluid. Lung scanning is a useful aid to diagnosis. The principal factors that have been implicated in the clinical syndrome of amniotic fluid embolism are anaphylaxis, vascular obstruction by particulate matter, vascular spasm due to prostaglandins and possibly some other vasoactive substances, and the possibility that all the changes could be explained by disseminated intravascular coagulation as a primary event. Further work is required to elucidate the relative contributions of these various factors. Due to the suddeness of the catastrophe and the very high mortality, haemodynamic data in humans is virtually non-existent. With improved methods of resuscitation it is to be hoped that the mortality rate will be reduced and that such data will become available. In this way it might become possible to apply the results of animal research and indicate the most effective method of treatment.