The relationship between variations of al-acid glycoprotein (orosomucoid, AGP) microheterogeneity detected from isoelectric focusing (IEF) patterns and clinical stage of acute inflammation based on serum C-reactive protein (CRP) levels and interleukin-6 (IL-6) levels was investigated. Serum samples were obtained from healthy subjects, and from patients with esophageal or stomach carcinoma before and after operation. Samples without neuraminidase treatment were used for AGP microheterogeneity analysis, and samples with neuraminidase treatment for AGP heterogeneity analysis. In AGP microheterogeneity, nine bands were detected in the range of p/3.18-3.57 in sera obtained from healthy subjects. In patients, AGP microheterogeneity changed the first day after operation; the percentage of bands surrounding p/3.5 increased, and the highest value appeared in sera taken the first or second day after operation and then decreased quickly. These bands showed reactivity for concanavalin Pc (Con A). The increase in Con A-reactive AGP occurred later than the increase in IL-6, and occurred earlier than the increase in CRP. On the seventh day after operation, the percentage of bands around p/3.2 increased. These bands showed the reactivity for Datura stramonium agglutinin. On the other hand, in samples with neuraminidase treatment, little change of AGP heterogeneity was observed in most samples, which did not reflect the stage of inflammation. These findings suggested that AGP microheterogeneity detection was a useful marker for the clinical stage of inflammation.