Mononuclear phagocytes can be activated to develop enhanced expression of a wide range of macromolecules and mediators. Amongst these are several procoagulants, most notably thromboplastin. A variety of stimuli (particles, ligands for cell surface receptors, and some pharmacological agents) enhance procoagulant expression. We indicate that such enhancement may contribute to intra-and extravascular coagulation in several types of infections. We also point to the paucity of knowledge on the biosynthesis and intracellular transport of these procoagulants and speculate on the nature of the mechanisms involved.