The method of Rathman and Christian for determining the micellar activities of dimethyldodecylamine oxide by pH titration in the presence of swamping electrolyte has been extended to accommodate nonswamping electrolyte conditions. Dimethyltetradecylamine oxide (AO(+)) was used as a model surfactant in this study. The effect of the added chloride on the critical micelle concentration (cmc) values of HAO(+) and AO(+/-) was experimentally determined and incorporated into the titration method. Under the experimental conditions used, the change in the cmc value of AO(+) was negligible while the cmc of HAO(+/-) changed logarithmically with increasing chloride concentration (slope = -0.58). Results show a dependency of the interaction parameter, a, between AO(+/-) and HAO(+) on the ratio of the initial chloride to surfactant concentrations. The pK(a) and cmc values are also reported. To overcome the need for experimentally determining the change in the cmc value of HAO(+) with respect to the added chloride concentrations, an approximation based on Hobbs＇ expression for the influence of monovalent counterions on the cmc of charged surfactants was employed. Resulting beta values using both the experimental and approximated equations differ by less than 5%.