Admicellar chromatography was studied for the mutual separation of pharmaceuticals. Admicellar columns were prepared by passing acetonitrile solutions containing dodecyltrimethylammonium chloride (DTAC) through a silica gel column (Mightysil Si 60). Successful separations of pharmaceuticals were achieved by optimizing the experimental conditions such as the pHs, DTAC concentrations, and acetonitrile fractions. For example, benzalkonium chloride was separated from benzethonium chloride with the use of 1.0% DTAC in 20% acetonitrile at pH 6. A DTAC aqueous solution (0.5%, pH 7) was successfully used for the mutual separation of sulfa drugs (e.g., sulfadiazine, sulfathiazole, sulfapyridine, and sulfamerazine). Methoxyphenols (o-, m-, and p-isomers) were separated from each other by using 0.5% DTAC in 5% acetonitrile at pH 5.