This study measured the incidence of recurrent aphthous ulcers during the use of dentifrices with and without sodium lauryl sulfate (SLS). A single-blind, crossover design was used. A statistically significant reduction in recurrent aphthous ulcers was observed during 2 months' use of SLS-free dentifrice compared to 2 months' use of the SLS-containing dentifrice. These results support the results of an earlier independent study, and suggest that use of an SLS-free dentifrice should be considered for individuals suffering from recurrent aphthous ulcers.