Abstract: Human serum CRP of patients pleural fluid was isolated by CPS （C-polysaccharide）-sepharo- se.purified by gel filtration on Ultrogel ACA 34 columm and adsorbed with anti-NHS （normal human serum）-sepharose.The product is of 98% pure,shows only one disc on both PAGE and SDS-PAGE.MW 120 KD.It is suggested that CRP is composed of 5 subunits. The electro-immunoassay of purified CRP in the concentration range of 0.06—1.0μg showed a very good linear relationship between the height of the rocket （mm） and the concentration of CRP （μg） with r=0.9997. The mean value of the CRP of 95 normal human sera assayed by this method was found to be 3.5μg/ml （middle value 2.2μg/ml）.Ninety percent of normal value is below 9.6μg/ml.and 95% below 12 μg/ml.which are somewhat higher than that of the values reported Possibly the deviation is due to the different methods of assay of proteins adopted.