This study compared the clinical efficacy of three mouthrinses containing either 0.12% chlorhexidine, phenolic compounds, or sanguinarine, which were used unsupervised, in a placebo-controlled, double-blind study of 6 months' duration. The study was conducted according to ADA clinical guidelines for evaluation of antigingivitis agents and was completed by 481 adults. Following baseline exams and a prophylaxis, subjects were randomly divided into treatment groups matched for age, gender, and gingivitis severity, and were instructed to use the rinses in accordance with manufacturer's directions. Followup examinations evaluated supragingival plaque, gingivitis, and gingival bleeding. Compared to placebo at 6 months, the group rinsing with 0.12% chlorhexidine had significantly less gingivitis (31% reduction), gingival bleeding (39% reduction), and plaque (49% reduction) and was significantly better than any of the other treatment groups (P less than 0.05). Both the phenolic and sanguinarine groups showed moderate, yet significant, reductions in plaque compared to placebo (24% and 12% respectively) yet were significantly less effective than the 0.12% chlorhexidine rinse (P less than 0.05). However, neither the phenolic nor sanguinarine rinses were significantly different than placebo in their effects on gingivitis or gingival bleeding. These results support previous published results on the superiority of 0.12% chlorhexidine when used in conjunction with professional care and as an adjunct to routine oral hygiene practices.