AbstractMicellar electrokinetic capillary chromatography has been explored as an efficient and rapid method of separating the photoproducts of 2′‐deoxyuridylyl‐(3′‐5′)‐thymidine (i.e.,cis‐synandtrans‐syncyclobutane dimers, (6–4) photoproduct, and the relatedDewarvalence isomer) from normal nucleosides and nucleotides. Three cationic surfactants, dodecyl‐, tetradecyl‐, and hexadecyltrimethy‐lammonium bromide were evaluated and the separations compared with those obtainable with the anionic surfactant, sodium dodecylsulfate. Optimum resolution of the dinucleoside monophosphate photoproducts was obtained using tetradecyltrimethylammonium bromide. By use of this detergent the photoproducts could also be separated from other normal constituents in less than 6 min at −25 kV. Dodecyl‐ and hexadecyltrimethylammonium bromide provided some separation between the various species but sodium dodecylsulfate did not separate the UV radiation‐induced products from either the parent compound or other dinucleoside monophosphates. Increased interaction between negatively charged solutes and positively charged micell