PCT was measured for patients in the intensive care unit of our hospital , who were divided into severe infection group , general infection group and non - infection group. [Results]: The levels of PCT in severe infection group were significantly higher than that innoninfection group.The positive rate of PCT was significantly higher than that of hemocultures in severe group and general infection group .There was significant correlation between serum PCT and prognosis.[Conclusion]: PCT is important guiding significance for the diagnosis of infection and evaluated prognosis in the critical patients.