There was no significant difference in the levels of factor XII between sick newborns and normal age-matched controls, although the levels of both groups were lower than normal older children. Detailed coagulation studies on 44 sick infants revealed 11 to have disseminated intravascular coagulation (DIC). In those with DIC, the mean Hageman factor was 20% and in those without DIC, 25% (P greater than 0.05). Rabbits given a constant infusion of lysozyme (which inhibits factor XII) showed laboratory evidence of endotoxin-induced DIC. The data suggest that neither reduced factor XII levels nor Hageman factor inhibition provided protection from DIC. The data further suggest that other coagulation pathways might be involved in order to elicit the DIC.