A commercially available antimicrobial mouthrinse was evaluated among students in Mexican boarding schools. The application was made daily for 3 months under the direct supervision of the project personnel. The observations indicated that the use of this mouthrinse decreased gingivitis substantially in comparison to the use of a control rinse which consisted of flavored water. It is concluded that this mouthwash, containing the known antimicrobial agents cetylpyridinium chloride and domiphen bromide, can be of clinical benefit if conscientiously applied as an adjunct in an oral hygiene regimen of regular toothbrushing with a dentifrice.