This study was carried out to investigate the frequency of E. gingivalis in the gingival crevices of patients with periodontitis compared to normal subjects. Flagyl therapy was tried in cases with periodontitis. Also the frequency of this amoeba was investigated in patients receiving chemotherapy to be compared to normal subjects. The results revealed that higher frequency was observed in patients with periodontitis and flagyl therapy reduced this frequency. Cases under chemotherapy showed higher frequency than the normal control. Histopathological sections from the gingiva of periodontitis patients did not show any amoeba invading the tissue.