Lysozyme activities in gingival exudate collected from patients with periodontal disease and from normal subjects were measured. The relationship between lysozyme activities and various clinical findings such as PMA-index by Schour and Massler, gingival index by Loe, debris index and calculus index by Greene and Vermillion, depth of periodontal pocket (mm), degree of tooth mobility and bone loss score (%) by Schei et al. were examined.Kakizaki's modified method was used to assay the lysozyme activity of gingival exudate collected by filter paper strip.The following results were obtained:1. The lysozyme activities were demonstrated and measured in all gingival exudate, and varied considerably with individuals.2. The lysozyme activity showed no disparity in age.3. The lysozyme activity of female was significantly higher than that of male, especially in periodontal patients (P<0.01).4. The lysozyme activity of periodontal disease group was remarkably higher than that of normal group, and had a tendency to increase according to the progression and aggravation of the disease, and showed significant difference among each clinical group.5. Statistically significant correlations were observed between the lysozyme activity and gingival index (P<0.01), PMA-index (P<0.001), pocket depth (P<0.001), tooth mobility (P<0.001), bone loss (P<0.001), and amount of exudate (P<0.05), except debris index and calculus index.It is concluded from these results that the lysozyme activity of gingival exudate is closely related to each clinical finding and process of periodontal disease.