In pH 6.0 citric acid-Na₂HPO₄ buffer solution goat-anti-human C reactive protein (CRP) was combinated with human CRP specifically, to aggregate with formation of immune complex particles that exhibited three resonance scattering peaks at 350, 390 and 440 nm respectively, in the presence of PEG-6000. The laser scattering measurement indicates that the average diameter of the immune complex particles is 1720.0 nm. CRP concentration in the range from 0.03 to 1.80 μg•mL^－1 is all proportional to the resonance scattering intensity at 390 and 440 nm. Its regression equation is ΔI_{390 nm}＝306.4c＋17.3 and ΔI_{440 nm}＝296.0c＋10.7, the correlation coefficient is 0.9993 and 0.9996, and the detection limit is 0.011 and 0.012 μg•mL^－1, respectively. The method has been applied to the determination of CRP in the human blood serum, and its results are in agreement with those of the immunoturbity, with relative standard deviation of 0.90%～4.12%.

Key words: C reactive protein, immune complex particle, immunoreaction, resonance scattering