Lectin histochemistry revealed that Kupffer cells in the normal liver bound lectins such as Concanavalin A (Con A), Ricinus communis agglutinin (RCA) and Wheat germ agglutinin (WGA), but did not bind Peanut agglutinin (PNA), Dolichos fibflorus agglutinin (DBA), Ulex europaeus agglutinin I (UEA-I) or Soybean agglutinin (SBA). Kupffer cells in viral liver diseases, however, bound the PNA lectin and the binding was specific to Kupffer cells in liver parenchyma. Computer image analysis was performed using light micrographs of sections stained with immunoperoxidase and diaminobenzidine (DAB). The dark brown area of reaction products was detected by analyzing each color component (red, green and blue) in the picture and was expressed as the percent area in the parenchyma. Quantitative analysis revealed the percent area occupied by Kupffer cells positive for the PNA lectin was as follows: acute hepatitis, 2.83 +/- 0.74; chronic persistent hepatitis, 2.51 +/- 0.88; chronic aggressive hepatitis, activity moderate and severe, 4.71 +/- 2.23 and 3.45 +/- 1.84; and liver cirrhosis, 1.96 +/- 0.99. The percent area of Kupffer cells was significantly higher in CAH2A than that in chronic persistent hepatitis or in liver cirrhosis. These results suggest that the PNA lectin could be used as a marker for activated Kupffer cells and that activated Kupffer cells were increased in volume in chronic aggressive hepatitis.