The blood of sufferers from ischæmic heart disease contains free ceramide, identified by physical and chemical methods. Other sources of identical or closely related ceramide include thromboplastin, snake venom, blood of some marsupials and, In general, dead tissue. Serum ceramide acts as a thromboplastic lipid; this effect Is counteracted by cholesterol. Connections between stress, free ceramide and coagulability are noted and discussed in relation to atherosclerosis. Applications of studies on free ceramides in biological matter are suggested.