A study has been made of micellar formation in ionic surfactant solutions in the presence of sodium chloride and a non-ionic surfactant. Experiments on sodium monolaurin sulfate (SMLS), preparation and properties of which have not been so far reported, reveal that the electrolyte reduces the critical micellar concentration of the surfactant solution. The dye-titration method gives a value of c.m.c. lower than that found by the conductance method; with increased electrolyte concentration, the difference in the two values gradually decreases to a small order. Conductance-concentration curves of ionic detergents with and without non-ionic additive suggest that on addition of non-ionic additive, mixed micelles are formed, in which hydrogen bonds are the main binding factors. While conductance of an anionic detergent solution increases, that of a cationic detergent solution decreases on minute addition of non-ionic detergent; in both the cases, the characteristic bend in the conductance-concentration curve tends to disappear gradually, for which plausible explanations are offered. © Copyright, 1960, by the American Chemical Society.