The present clinical trial was performed to assess the effect of a Sanguinarine-containing mouthrinse on developing plaque and gingivitis in man. The trial was designed as a blind cross-over study. The active mouthrinse consisted of a 0.03% aqueous solution of Sanguinaria extract; an aqueous solution with similar color and taste as the active rinse was used as the placebo preparation. 14 dental students participated in the trial. At the start of each of 2 test phases, their gingival conditions were normal and their tooth surfaces free from dental plaque. Following a baseline examination, the participants refrained from mechanical tooth cleaning measures for 2 weeks. They rinsed twice daily with either the active or the placebo mouthrinse. Clinical examinations of plaque and gingivitis were repeated after 4, 7 and 14 days use of the mouthrinse preparation. During the second test phase of no mechanical tooth cleaning, the subjects who previously had rinsed with the placebo solution now used the active compound and vice versa. The results demonstrated that the Sanguinarine-containing mouthrinse was effective in reducing plaque formation and retarding the development of gingivitis.