Sodium lauryl sulphate (SLS) is used in toothpaste and mouth rinses as an emulsifying and surface cleaning agent. SLS has been implicated in an increased incidence of oral irritation in subjects predisposed to recurrent aphthous stomatitis (RAU). Hence, the purpose of this study was to determine the levels of SLS found in the oral cavity following rinsing with an SLS containing mouth rinse and brushing with a SLS containing dentifrice. An analytical method to separate SLS from saliva and other complex systems was developed. The method used high performance liquid chromatography (HPLC) and detection performed using conductivity measurements. Standard curves with known concentrations showed a detection limit of less than 0.4 ug SLS/ml of fluid. 2 clinical studies were conducted to determine the amount of SLS retained in the mouth by a healthy population after rinsing or brushing with commercially available products. The results showed, after rinsing, that 96% of the available SLS from the rinse was recovered in the collected samples within 2 min. Similarly, after brushing, 86% of the SLS contained within the toothpaste was recovered from the collected samples within the first 10 min. These results showed that the amount of SLS retained in the oral cavity was minimal and the contact time between SLS and the oral cavity was very short. A 2nd study was conducted to measure the amount of SLS retained in the mouth by a population susceptible to RAU. After rinsing, 97% of the available SLS was recovered within the first 2 min. Following brushing, 89% of the SLS in the dentifrice was recovered within the first 10 min. These results were comparable to those determined by the study involving the healthy population.