Clotting factors and platelets were measured in 19 patients with acute meningococcal infection. Good evidence of diffuse intravascular coagulation was found in 5 patients and equivocal evidence in a 6th patient. Each of these patients had fulminant meningococcemia with profound endotoxin shock. Twelve patients, with less overwhelming meningococcal infection, exhibited neither severe hypotension nor clear-cut evidence of intravacsular coagulation. Finally, a unique, severely ill patient had an endogenous anticoagulant probably secondary to unrelated autoimmune disease. He had thrombocytopenia suggestive of the release of a large amounts of meningococcal endotoxin but no evidence of intravascular coagulation and only moderate hypotension. Five patients with profound endotoxin shock received heparin as part of their therapy for shock. Three patients, given heparin late in their course, died in irreversible shock. A 4th patient came out of shock but died later of cardiac arrest. A 5th patient, who received heparin early, survived. This study establishes that intravascular coagulation and irreversible shock occur together in fulminant meningococcemia but does not establish whether these are independent or related manifestations of severe meningococcemia. Further experience, especially with heparin, is needed to determine if intravascular coagulation contributes to the irreversibility of shock in fulminant meningococcemia.