The purpose of this study was to evaluate the clinical application of strips containing 10% Tetracycline (TC) in periodontal disease. In this double blind study, placebo strips, which did not contain TC, were also prepared. Ninety-two sites in 46 cases with greater than a 4 mm periodontal pocket were randomly assigned to experimental and control study groups. The following clinical parameters at each site were recorded at Weeks 0, 1, 2 and 3 after insertion of the LSD or placebo strip: plaque and calculus score, probing depth, gingival inflammation (redness, swelling, bleeding on probing, pus discharge), mobility of the tooth, pain on insertion of strip and pain after the procedure. The residual quantity of TC in the periodontal pocket was also determined at 1, 2 and 7 days after inserting the LSD. All clinical data was evaluated using 3 types of statistical test (X2 test, Mann-Whitney's U test and Wilcoxon's test). Thus, the following results were obtained: 1. The LSD group showed much improvement in clinical condition compared with the placebo group. 2. The conditions of bleeding, redness or swelling of gingival tissue were much improved in the LSD group, even after data evaluation with all 3 types of statistical test. 3. The residual quantity of TC was decreased day by day until finally it was not recognized in the 7 day samples. 4. This study suggested that the application of LSD in the periodontal pocket could be effective in periodontal treatment.