In order to determine the relationship between probing pocket depth and trypsin like activity in subgingival plaque, probing pocket depth and loss of attachment were measured by Michigan 0 probe on mandibular incisors of 30 patients with adult periodontitis. And the trypsin like activity of Treponema denticola, Porphyromonas gingivalis, and Bacteroides forsythus was evaluated by the hydrolysis of N Benzoyl DL Arginine 2 Naphthyla mide (BANA) using PerioScan reagent cards(Oral B Laboratories, Redwood City, CA). The obtained data were statistically analyzed by Microstat program. The results were as follows. 1. The number of teeth showing negative trypsin like activity was more in shallow periodontal pocket groups, but the number of teeth showing positive trypsin like activity ivas morc in deep periodontal pocket groups. 2. There was a significant positive correlation between probing pocket depth and trypsin like activity in subgingival plaque(y=0.413X 0.955, r = 0.7024, p<0.001). 3. There was no consistent relationship between loss of attachment and trypsin like activity in subgingival plaque(p > 0.01).