The purpose of this investigation was to determine the effects of two commercial mouth rinses, ListerineR and ViadentR, on bacterial plaque and gingivitis. over a sixweek period, 24 adults, ages 18-41, were examined for the amount of bacterial plaque and level of gingivitis using Silness and toe\u27s Plaque Index (PLI) and Gingival Index (GI). At the beginning of each two week period, subjects were examined for the amount of plaque and level of gingivitis and given a different mouthrinse: appointment one--viadentR (mouthrinse A), appointment two--placebo mouthrinse (mouthrinse B), and appointment three--ListerineR (mouthrinse C). Additionally, subjects were given oral and written mouthrinsing instructions at each appointment. A double-blind, cross-over design was used in this experimental pre-test/post-test research study. Results were tabulated on the basis of change in the mean Plaque and Gingival Index scores. Data were examined using a one-way analysis of variance and Tukey\u27s studentized Range Test to determine if any statistically significant differences existed in the mean GI scores and PLI scores throughout all four appointments. Additionally, a Paired-Difference t-test was applied to data to determine if the independent variables, ViadentR mouthrinse and ListerineR mouthrinse, had a statistically significant effect on the dependent variables, gingival inflammation and bacterial plaque. Results showed that rinsing with either ViadentR or ListerineR mouthrinse as an adjunct to routine oral hygiene had no statistically significant effect on the level of gingivitis or the amount of bacterial plaque