Summary Forty-six pediatric patients with proved bacterial septicemiahad platelet counts and coagulation factor assays performed. Eighteen of 33 children with gram-negative and 10 of 13 patients with gram-positive sepsis had platelet counts below 150,000/mm3. Of the 28 with thrombocytopenia, seven had DIC, 10 had probable DIC, but 11 had no other laboratory evidence to suggest DIC as the cause. Since thrombocytopenia was present in patients without DIC, other etiologic factors may be involved. The platelet count can be a useful diagnostic aid in infants with septicemia.