The ultimate goal of periodontal therapy is the regeneration of periodontal tissue which has been lost due to destructive periodontal disease, and numerous kinds of materials and techniques have been developed to achieve this goal. Bone grafts include autografts, allografts, xenografts and synthetic grafts. Among the synthetic grafts, bioactive glass has been used in dentistry for more than ten years and Fetner reported improved new bone formation and more amount of new attachment after grafting PerioGlas , a kind of bioactive glass, in 2-wall defects of monkeys in 1994. It is well known that 1-wall defects have less osteogenic potential and more epithelial migration, so we need to study the effect of bioactive glass in 1-wall defects in dogs. The present study evaluates the effect of bioactive glass on the epithelial migration, alveolar bone regeneration, cementum formation and gingival connective tissue attachment in intrabony defects of dogs. Four millimeter deep and four millimeter wide 1-wall defects were surgically created in the mesial aspects of premolars. The test group received bioactive glass with a flap procedure and the control underwent flap procedure only. Histologic analysis after 8 weeks of healing revealed the following results: 1. The height of gingival margin was 1.30+/-0.73mm above CEJ in the control and 1.40+/-0.78mm in the test group. There was no statistically significant difference between the two groups. 2. The length of epithelial growth(the distance from CEJ to the apical end of JE) was 1.74+/-0.47mm in the control and 1.12+/-0.36mm in the test group. There was a statistically significant difference between the two groups(P<0.01) 3. The length of new cementum was 2.06+/-0.73mm in the control and 2.62+/-0.37mm in the test group. There was no statistically significant difference between the two groups. 4. The length of new bone was 1.83+/-0.74mm in the control and 2.39+/-0.59mm in the test group. There was no statistically significant difference between the two groups. These results suggest that the use of bioactive glass in 1-wall intrabony defects has significant effect on the prevention of junctional epithelium migration, but doesn't have any significant effect on new bone and new cementum formation.