Eight episodes of clinical septicemia in five children were assessed using C-reactive protein (CRP) determinations. The measurements were performed turbidimetrically, with quantitative results available in less than 10 minutes. Three patients had epiglottitis, one had recurrent septicemia secondary to severe underlying illnesses and one patient was followed postoperatively after open heart surgery. Regardless of etiology septicemia was consistently associated with a rapid increase (greater than or equal to 20 to 214 mg/liter) in the CRP concentration. Elevated values were obtained 5, 13 and 16 hours after the onset of symptoms of epiglottitis. When determined the CRP level was invariably elevated at the time of the first positive blood culture. CRP determinations in patients with symptoms of septicemia would have supported the diagnosis at least 24 hours before the positive blood culture. In addition, sequential CRP measurements proved beneficial in monitoring the course of septicemia.