The objective of the present clinical trial was to assess the efficacy of mouthwashes containing antiseptic agents on established and developing plaque and periodontal disease in adult subjects using a newly described clinical research model. The study was carried out in 21 patients with periodontal disease. At the baseline examination, all tooth surfaces-sites were studied with regard to dental plaque, gingivitis, bleeding on probing to the base of the pocket and probing pocket depths. The patients were subsequently randomly assigned to 1 of 3 groups, each consisting of 7 individuals. Group A rinsed with a 0.01% solution of Sanguinarine, group B rinsed with a 0.2% solution of chlorhexidine and group C rinsed with a placebo solution. No instructions regarding mechanical plaque control measures or information regarding the etiology and pathogenesis of periodontal disease were given to any of the patients during the course of the 6-weeks of trial. The clinical examination was repeated after 2 weeks use of the mouthwash preparations. Following the re-examination, all patients were subjected to scaling and root planing in 2 jaw quadrants chosen at random. After another 2 weeks, the 2nd re-examination was performed and the teeth in the 2 remaining jaw quadrants were thoroughly scaled. The final examination was performed 2 weeks later. During the 4 weeks of rinsing, without adjunctive professional mechanical debridement, the frequency distribution of plaque Index scores 2 + 3 did not change in the group of patients using the placebo solution, but was significantly reduced in both the chlorhexidine and the Sanguinarine groups.(ABSTRACT TRUNCATED AT 250 WORDS)