In this study, I made a monoclonal antibody, using the mandibular condylar cartilage as antigen. By light microscopic immunocytochemical observations, this antibody reacted with the chondrocytes both in the mandibular condyle and the costal cartilage, hepatocytes and skeletal muscle cells. By electron microscopic immunocytochemical observations, reaction products (gold particles) were seen on the glycogen particles in the chondrocytes. Further, by dot blotting assay, this antibody was found to react directly with the purified glycogen. Meanwhile, all these reactions disappeared after a-amylase digestion. These results indicate that this antibody specifically recognizes glycogen or glycogen-related sugar chains. Therefore, I think that this antibody is very much useful for detecting the glycogen instead of the PAS reaction, since PAS reaction is not a specific method to detect the glycogen.