Protein C replacement therapy with a monoclonal antibody purified, virus inactivated protein C concentrate was carried out in nine infants (three male, six female) with severe congenital protein C deficiency and life-threatening purpura fulminans and/or thrombosis associated with disseminated intravascular coagulation (DIC). Eight infants were homozygous for protein C deficiency; one was a compound heterozygote. The treatment period varied from 22 days to three years. The half-life of protein C was found to be as short as two to three hours during activation of the coagulation system, increasing to approximately ten hours after stabilization. During the acute phase, protein C levels of 0.10 to 0.25 IU/mL were associated with elevated markers of coagulation activation indicating DIC, while protein C levels greater than 0.25 were associated with normalization of coagulation markers. No product-related side effects were reported. Episodes of bleeding or purpura recurred in all patients who were switched to oral anticoagulant therapy, necessitating reinstatement of protein C replacement therapy, either as needed to control symptoms, or on a long-term prophylactic schedule, alone or in addition to oral anticoagulation. Home treatment with protein C concentrate allowed a near-normal life-style for patients who otherwise would be hospitalized for long periods of time.