The purpose of the study was to compare the efficacy of four mouthrinses in clinical outcomes of changes in oral malodor measurements in a 4-week, randomized, double-blind, longitudinal clinical trial in adults. The four rinses were coded as Products 1, 2, 3, and 4 so that neither the examiners nor subjects had the knowledge of treatment. Of the four mouthrinses, two were commercially available mouthrinses with essential oils (EO) or chlorine dioxide plus zinc (CD/Zn) as active ingredients (Products 1 and 4), one mouthrinse was a formulation containing cetylpyridinium chloride (Product 2), and one was a placebo (Product 3). A total of 99 subjects who met the study criteria were assigned randomly to one of the four groups. At three separate visits (0, 2, and 4 weeks), subjects received an examination of the oral soft tissues and were assessed for baseline oral malodor by two organoleptic judges and a laboratory instrument that measures oral malodor. Subjects were instructed to use the assigned rinse, and the measurements were performed again after 2 and 4 hours. Throughout the 4-week study period, each subject was asked to use the assigned rinse twice daily per the manufacturer's recommended directions. The results showed that the four mouthrinses reduced oral malodor within 4 hours after a single usage, with Product 2 being the most effective and the placebo being the least effective. Daily use of EO, CD/Zn, and placebo rinses for up to 4 weeks did not reduce oral malodor from week 0 baseline values, and the effects on oral malodor were comparable among these three mouthrinses. Product 2 was the only mouthrinse that reduced oral malodor from baseline values after 2 and 4 weeks of daily use.