Objective To evaluate the diagonosis value of serum procalcitonin(PCT),C-reactive protein(CRP)and lipopolysaccharide(LPS)in patients with community acquired pneumonia(CAP).Methods From Nov.2004 to Feb.2005,PCT were determined by Brahms PCT-Q;CRP were measured by using immunity-turbidity method;LPS were measured by enzyme linked immunosorbant assay(ELISA)and white blood cells were counted in serial blood samples from 36 patients with community acquired pneumonia and compared with the 18 healthy people.Results For PCT,CRP,LPS,WBC count,the sensitivities were 80%,92%,94% and 47.2%,and the specificities were 88%,64%,30%and 95%respectively for the diagnosis of 36 patients with CAP.The mark of PCT in the medium and serious CAP group(Ⅰ、Ⅱ Fine's risk classification)were significantly higher than those in the light CAP group(Ⅲ、Ⅳ、Ⅴ Fine's risk classification)(P