This study was performed to elucidate the histopathologic distribution of immunoglobulins, particularly IgA, IgG and IgM in the periapical lesions, including 22 periapical granulomas and 18 periapical cysts. The immunoperoxidase staining method using reagents manufactured and supplied by Danish DAKO company was employed in this study. In comparison with the immunohistochemical methods, this method was proved to be reliable and convinient one to detect immunoglobulins in the tissue. The following results were obtained: 1. In the 22 periapical granulomas, IgG was found in 20 cases (90.9%), IgA in 16 cases (72.7%) and IgM in 19 cases (86.3%). 2. In the 18 periapical cysts, IgG was found in 16 cases (88.8%), IgA in 13 cases (72.2%) and IgM in 15 cases (83.3%). 3. The distribution of immunoglobulins both in periapical granulomas and periapical cysts was in great diversity according to the lesion and area. 4. More immunoglobulins were found in the exudative area with moderate or severe infiltrations of plasma cells and lymphocytes and less concentration of immunoglobulins were seen in the area with leukocytes infiltration and tissue destruction. 5. The area with collagenolysis and reparative activity contained more abundant IgG and IgM than IgA in periapical granulomas. 6. IgG was dominant in the granulomatous connective tissue and immunoglobulins were not easily found in the fibrous capsule in periapical cysts.