THE RELEASE OF CHLORHEXIDINE FROM an ethyl cellulose-based dosage form (SRD) has been shown to be effective in the reduction of the flora associated with periodontal pockets as well as in reducing probing depths. In this study, treatment with this dosage form was compared to routine maintenance therapy (RMT) in a 2-year, split mouth clinical trial. Ten patients with 84 pockets greater-than-or-equal-to 5 mm who had not received any periodontal therapy or systemic antibiotics over the last 6 months were included. The patients all received a full mouth scaling and root planing together with thorough oral hygiene instruction. Two months later (baseline) plaque index (PII), bleeding on probing (BOP), pocket probing depth (PD), and attachment levels (AL) were assessed at all selected sites. Pockets on the control side then received RMT while the experimental pockets were treated with the SRD only. Treatment was repeated every 3 months for 2 years. The SRD treatment resulted in an improvement of greater-than-or-equal-to 3 mm in PD of at least 1 pocket in 8 of 10 patients, while RMT resulted in a similar improvement in only 1 of 10 patients (P = 0.012). Similarly a gain of attachment of greater-than-or-equal-to 3 mm was found in at least 1 SRD pocket in 8 of 10 patients. The RMT resulted in a similar improvement in only 2 patients (P = 0.012). The reduction in PD (P = 0.01) and gain in AL (P < 0.03) as compared to baseline were significantly greater for SRD treatment than for RMT at all time periods. BOP showed significant differences at 9, 15, 21, and 24 months only (P < 0.05). These results indicate that the SRD treatment provided significantly better results than RMT for maintenance of deep pockets over a 2-year period.