In order to study the effects of NO, endothelin (ET), substancep (SP) and caleiton gene-related paptide (CGRP) immunoreactive substances in chronic periodontitis tissue and the relationship with periodontitis, immunohistochemical and histochemical staining methods were used respectively to detect the expression of the above immunoreactive substances in 20 patients with chronic periodontitis. Quantitative analysis showed that NO and ET in periodontitis tissues were increased significantly (P < 0.01), particularly the content of ET, in comparison to normal tissue. Due to the increase of ET content, the bolld supply was diminished and influenced the periodontal tissue by causing tissue damage. This study suggests that NO and ET immunoreactive substances are closely associated with periodontitis and may play an important role in the disease. There were no marked changes on SP and CGRP.