The efficacy of a chlorine dioxide-containing mouthrinse in reducing oral malodor was compared to that of a water control in randomized, double-blind crossover study in 12 male and female subjects. Entrance criteria required a score of < or = 1 (slightly unpleasant/stale) on a 7-point ordinal odor pleasantness scale at both screening and baseline. On the test mornings, subjects refrained from oral hygiene and rinsed with 15 mL of either mouthrinse or water (one occasion each), under supervision for a timed 30-second interval. Three trained, previously calibrated sensory judges independently evaluated mouth odor pleasantness and intensity. Odor pleasantness scores (7-point scale) and odor intensity scores (5-point scale) from the three sensory judges were analyzed using an Analysis of Variance. The average score of all the judges was analyzed for each time point. The mean (+/- SD) mouth odor pleasantness in the chlorine dioxide group improved from -1.25 +/- 0.29 at baseline to -0.72 +/- 0.31 at 0.5 hour, -0.81 +/- 0.26 at 1 hour, -0.61 +/- 0.45 at 2 hours, and -0.61 +/- 0.55 at 4 hours post-rinsing (delta = 0.53, 0.44, 0.64, and 0.64, respectively). In the control group, the mean (+/- SD) mouth odor pleasantness improved from -1.06 +/- 0.40 at baseline to -0.94 +/- 0.58 at 0.5 hour, and to -0.97 +/- 0.46 at 1 hour, then deteriorated from -1.06 +/- 0.40 at baseline to -1.11 +/- 0.38 at 2 hours, and -1.08 +/- 0.61 at 4 hours post-rinsing (delta = 0.11, 0.08, -0.06, and -0.03, respectively). The mean (+/- SD) mouth odor intensity in the chlorine dioxide group improved from 1.14 +/- 0.17 at baseline to 0.92 +/- 0.35 at 0.5 hour, 1.06 +/- 0.24 at 1 hour, 0.83 +/- 0.44 at 2 hours, and 0.81 +/- 0.44 at 4 hours post-rinsing (delta = -0.22, -0.08, -0.31, and -0.33, respectively). In the control group, the mean (+/- SD) mouth odor intensity improved from 1.11 +/- 0.26 at baseline to 0.97 +/- 0.44 at 0.5 hour and 1.03 +/- 0.33 at 1 hour, then deteriorated from 1.11 +/- 0.26 at baseline to 1.17 +/- 0.39 at 2 hours, and 1.19 +/- 0.52 at 4 hours post-rinsing (delta = -0.14, -0.08, 0.06, and 0.08, respectively). Analyses of Variance showed that improvement in mouth odor pleasantness compared to baseline for the chlorine dioxide-containing mouthrinse versus the water control was statistically significant (p < 0.05) at all post-rinsing evaluations. For the reduction in mouth odor intensity, there was a statistically significant difference favoring the oral rinse at 2 and 4 hours post-rinsing. Thus, this study demonstrates that a one-time use of a chlorine dioxide-containing mouthrinse significantly improves mouth odor pleasantness and reduces mouth odor intensity for at least 4 hours.