A coumarin-responsive chronic relapsing purpura fulminans syndrome is described in a protein-C-deficient newborn infant. Episodes of acute disseminated intravascular coagulation (DIC) and cutaneous gangrene, which first appeared at age 11 h, were effectively controlled for 28 months with transfusions of fresh-frozen plasma. Cryoprecipitate and cryoprecipitate-poor plasma induced remissions as long as those induced by fresh-frozen plasma (less than or equal to 72 h). Coumarins sustained a cryoprecipitate-induced remission for 19 days: they were then electively discontinued and 17 h later the patient had an acute exacerbation of DIC with haemorrhaging. Family studies showed protein C levels of 31-40% in the subject's symptom-free mother and full and half brothers. DIC, the coumarin effect, and the inherited protein C abnormality appear to have contributed to the extremely low plasma levels (less than or equal to 6%) of protein C in the patient. This experience suggests that protein C deficiency may greatly compromise the ability of newborn infants to control consumptive disorders.