The purpose of this study was to evaluate the systemic and local production of immunoglobulins and their levels in patients with periapical cysts using Enzyme - Linked Immunosorbent Assay. Streptococcus sanguis, Bacteroides gingivalis, and Bacteroides intermedius were grown for use as antigen and they were harvested by centrifugation. The patients were divided into two groups: patients of periapical cysts and normal control. 5 patients of each group were selected and their blood were obtained via intravenous puncture prior to surgical operation. Sera were prepared by centrifugation of each blood samples. Cyst fluid were aspirated from cystic cavity and cyst wall were excised at operation. Control tissue were also excised at extraction site of impacted wisdom teeth from normal control. Each tissue was prepared by homogenization and centrifugation. Then antibodies of each sample were measured by modified ELISA. The following results were obtained: 1. Serum IgG and IgM levels were not significantly different between patients with periapical cyst and normal control. 2. IgG and IgM levels of cyst fluid to Bacteroides gingivalis and Bacteroides intermedius were significantly higher than those of serum of patients with periapical cyst, but there was no significant difference to Streptococcus sanguis. 3. IgG and IgM levels of cyst wall to Bacteroides gingivalis and Bacteroides intermedius were significantly higher than those of control tissue, but there was no significant difference to Streptococcus sanguis. 4. IgG and IgM levels in cyst fluid and IgG levels in cyst wall were highest to Bacteroides gingivalis, and IgM levels in cyst wall were highest to Bacteroides intermedius.