Delmopinol, a 3-alkyl substituted N-hydroethyl morpholine, has shown potential as a mouthrinse for the management of dental plaque and treatment of gingivitis. Delmopinol has been shown to possess plaque inhibitory activity in several previous studies. The aims of this study were to: 1) compare the antiplaque, antigingivitis efficacy and safety of 0.1% and 0.2% delmopinol-containing mouthrinses (DMP) in a 2-week, randomized, parallel arm, vehicle controlled study; and 2) determine if a dose response antiplaque, antigingivitis effect could be found in this type of formulation. One hundred and thirty-three male subjects were randomly assigned to one of three groups, 0.1% DMP, 0.2% DMP, or vehicle control mouthrinses. At baseline all subjects received a clinical examination consisting of an intraoral soft tissue, plaque (Turesky modification of Quigley-Hein plaque index), and gingival index (modified gingival index) evaluations, and received a thorough oral prophylaxis. All subjects refrained from all forms of oral hygiene for the next 2 weeks, except for the use of the assigned mouthrinse. Subjects rinsed for 1 minute with their assigned mouthrinse twice daily under supervision for 2 weeks. Following 2 weeks of mouthrinse use, plaque and gingivitis scoring and soft tissue examinations were repeated. The results showed the mean plaque index at the 2-week examination was statistically related to the baseline value (P < 0.0003, ANOVA) and the concentration of DMP (P < 0.0001, ANOVA). In contrast, the gingivitis index was not related to the concentration of DMP (P > 0.05, ANOVA). No adverse effects were noted or reported during this clinical trial.