The primary purpose of this study was to determine the safety and effectiveness of alexidine in the control of plaque and gingivitis in humans. For six months, 207 persons who continued their usual oral hygiene procedures rinsed twice daily with 15 ml of either alexidine (0.035% or a placebo solution. At the 30-day examination and for the remainder of the study, a statistically significant reduction in plaque between the two groups was recorded. Gingivitis was reduced in persons in both the test and placebo groups (the former always had the greater reduction), and a statistically significant difference was found at the 30-day and 90- day examinations. The preponderance of data indicates that, under the described experimental conditions, the alexidine rinse was effective in reducing both indicators of oral health and it may have important therapeutic potentials.