A double-blind, 3-week, randomized, placebo-controlled, parallel-group clinical trial was conducted to evaluate the tooth-whitening efficacy of a novel nontray, "paint-on" liquid whitening gel containing 18% carbamide peroxide (Colgate Simply White Clear Whitening Gel). Efficacy was based on measured Vita tooth-shade scores collected at baseline and after 2 and 3 weeks of product use. Eighty healthy volunteers were balanced into 2 groups based on gender, age, and shade scores (A3 or higher). The duration of product usage was 30 minutes, twice daily, for 3 weeks. Results from this clinical study showed that subjects' teeth in the liquid whitening gel-treated group exhibited an overall mean 3.84-shade improvement and a 3.5-shade difference compared with teeth in the placebo gel group (statistically significant, P < .05) after 3 weeks. Furthermore, this improvement exceeds the minimum requirement to claim "clinical efficacy" as established by the "Guidelines for the Acceptance of Peroxide-Containing Oral Hygiene Products," published by the American Dental Association in 1994. Therefore, it can be concluded that Colgate Simply White Clear Whitening Gel significantly whitens teeth.