Glutathione(GSH),a tripeptide thiol, found in virtually all cells, functions in metabolism tranasport and cellular protection. It protects cells against the destructive effects of reactive oxygen intermediates and free radicals. Also ${gamma}-Glutamyl$ transpeptidase(${gamma}-GTT$), an enzyme of major importance in GSH metabolism, initiates GSH degradation. In order to explore the $GSH-{gamma}-GTT$ system as periodontal disease activity indicator, we observed the ${gamma}-GTT$ and arachidonic acid metabolits according to clinical groups(Control, Adult periodontitis, Rapidly progressive Periodontitis). From the experiments, the following results were obtained. 1. When compared with normal, ${gamma}-GTT$ of A. P. and R. P. P. were increased, and only the change of ${gamma}-GTT$ of R. P. P. was statistically significant(P<0. 05). 2. The amounts of arachidonic acid metabolites were not different with statistical significance among the clinical groups. 3. ${gamma}-GTT$ may by useful adjuncts as new cytoprotective indicator and periodontal disease activity indicator in accordance with positive corelation pocket depth, attachment level and ${gamma}-GTT$.