The purpose of this investigation was to evaluate the clinical efficacy of controlled-release tetracycline fiber therapy in adult periodontitis patients. One hundred-twenty-two (122) adult patients from 3 dental centers were enrolled at baseline for this study. each patient provided at least one site in each of four quadrants that was > or = 5 mm and bled on probing. One or two such sites were selected as test sites and were randomly assigned to receive one of four treatments: scaling and root planing (S), scaling and root planing plus tetracycline fiber for 10 days (SF), fiber therapy alone for 10 days (F), or two 10-day serial fiber applications (FF). After treatment, no periodontal maintenance or supportive care was provided until the end of this 12-month study. Probing depth (PD), clinical attachment level (CAL), plaque, and bleeding on probing (BOP) were measured at baseline and at 1, 3, 6, 9, and 12 months following treatment. Repeated PD and CAL measurements were taken at three locations within each site and averaged for each site. One hundred-sixteen (116) subjects completed the study. All treatments resulted in similar improvements in clinical parameters compared to baseline and were equally effective in the treatment of periodontitis as measured by probing depth reduction, clinical attachment level gain, and reduction of bleeding on probing. The clinical response, established primarily by 3 months following therapy, was generally sustained in all treatment groups for 12 months without the benefit of supportive maintenance therapy.