OBJECTIVE The objective of this study was to examine the ability of three CPC-containing mouthwashes to kill planktonic bacteria in an in vitro short-exposure assay. METHODS This blind study was conducted on two common oral bacterial species: Aggregatibacter (Actinobacillus) actinomycetemcomitans and Streptococcus mutans. The following mouthwashes were tested: two containing 0.075% CPC and 0.05% NaF in an alcohol-free base, and one containing 0.075% CPC and 0.05% NaF plus 6% alcohol. Additionally, a 0.05% NaF-only mouthwash was included as a negative control. Bacteria were exposed to one of the test mouthwashes for 30 seconds and then washed thoroughly, serially diluted, and plated on appropriate media to determine viable bacterial counts. Viable counts were converted to a log reduction in colony forming units (CFUs) relative to the negative control. RESULTS All three test mouthwashes included in this study gave a statistically significant reduction of > 3 log CFUs relative to samples treated with the negative control. CONCLUSIONS All three experimental 0.075% CPC mouthwash formulas gave a > 99.9% reduction in viable bacteria of both species following 30 seconds of treatment.