Abstract: Polyethylene glycol precipitation-atravielet pliotometric assay (PPUPA) was employed to measure the concentration cf CIC in 40 healthy controls (HC),50 patients with acute allergic vasculitis (AAV) and 23 patients recovered from allergic vasculitis (RAV),and the concentration of CIC was compared with analysis of variance and Q test.The results showed that the value of CIC was significantly higher in AAV than that of HC and RAV (both P <0.01),and there was on significant difference between that of HC and RAV (P>0.05).By PEG precipitation-NS disolution-single radial immunodiffusion,some components in CIC were determined in 40 HC,49 AAV and 23 RVA.The early skin lesions of 43 paeients with AAV were examined by DIF,of them vascular immunoreactants were observed in 23 (53.5%).With p:fired enumeration data X² test comparisons of the components in CIC with those observed in DIF showed that there were no significant differences of IgA and C3/C3c (both P >0.05),but there was significant disparity of IgM in CIC and DIF results (P<0.01).No patient without IgM in CIC had Ig1Z in DIF.It is appropriate to deduce that that some components in CIC are closely related to the vascular immunoreactants detected by DIF.The results of this study support the hypothesis that CIC probably plays a major sole in the pathogenesis of AV,and that the concentration of CIC measured by PPUPA may serve as an indicator for assessing the therapeutic effect and estimating the prognosis of AV.