New improved types of analytical columns Zorbax Eclipse XDB-C18 (75 mm x 4.6 mm i.d., 3.5 microm) and Zorbax Eclipse XDB-C18 (50 mm x 4.6 mm i.d., 1.8 microm) have been tested for determination of estradiol (active substance), methylparaben, propylparaben (preservatives) and estrone (degradation product) and compared with the conventional C18 columns (250 mm x 3.0 mm i.d., 5.0 microm). The Zorbax columns differ with their particle size, column length and ODS (octadecylsilica) type as well. Higher flow-rates (up to about 2.5 ml min(-1)) could be applied regardless to back-pressure. The analysis - previously done at 40 degrees C - could be performed even at ambient temperature. Analytical run was shortened to 3.5 min (from 12 min used for the conventional C18 column) with the same or better retention characteristics. System suitability data for all Zorbax columns show the advantages of these columns for the practical use in routine quality control of pharmaceuticals, particularly from the point of view of speed of analysis and solvent consumption.