A rapid and simple liquid chromatographic procedure that uses micellar mobile phases, containing only sodium dodecyl sulfate (SDS) and phosphate buffer, is reported for the determination of some thiazide diuretics (althiazide, bendroflumethiazide, chlorothiazide, cyclothiazide, hydrochlorothiazide, hydroflumethiazide and trichloromethiazide) in pharmaceuticals. An interpretive optimization procedure, based on an equation that relates the capacity factor with the micellar concentration, indicated the SDS concentration at which the diuretics were best resolved. The determination of hydrochlorothiazide and trichloromethiazide in pharmaceuticals could be achieved with a micellar mobile phase of 0.02 mol l^–1 SDS in 0.01 mol l^–1 phosphate buffer (pH 7), with retention times below 5 min, but the determination of althiazide and bendroflumethiazide required a micellar mobile phase of 0.15 mol l^–1 SDS at the same pH, with retention times below 7 min. The recoveries from the pharmaceuticals were in the range 97.2–104.0%. The results were compared with those obtained with methanol–water mobile phases.