One-hundred forty-nine (149) healthy adult subjects completed a single-use, supervised trial, and 143 subjects completed a 6-week trial to determine the effect of rinsing with Plax prebrushing mouthrinse on supragingival plaque reduction. During the single-use trial, plaque was scored both initially and after subjects rinsed with Plax or a negative control rinse and then brushed with a dentifrice. Following a dental prophylaxis subjects then began a "home-use" phase of rinsing prior to normal brushing, twice daily for 6 weeks, at which time plaque was rescored. In the single-use trial, Plax and control rinses produced 21% and 22% reductions in plaque scores respectively. In the 6-week trial, Plax and control rinses produced 10% and 11% reductions in plaque scores respectively. In all cases, Plax was no more effective than the control rinse in enhancing the plaque-removal effectiveness of toothbrushing.