Arapid and sensitive RPHPLCmethod was developed for the routine control analysis of eletriptan hydrobromide and its organic impurity UK 120.413 in Relpax? tablets. The chromatography was performed at 20?C using a C18 XTerra ? (5 ?m, 150 x 4,6 mm) column at a flow rate 1.0 ml/min. The drug and its impurity were detected at 225 nm. The mobile phase consisted of TEA (1 %) - methanol (67.2:32.8 v/v), the pH of which was adjusted to 6.8 with 85 % orthophosphoric acid. Quantification was accomplished by the internal standard method. The developed RP HPLC method was validated by testing: accuracy, precision, repeatability, specificity, detection limit, quantification limit, linearity, robustness and sensitivity. High linearity of the analytical procedure was confirmed over the concentration range of 0.05 - 1.00 mg/ml for eletriptan hydrobromide and from 0.10 - 1.50 ?g/ml for UK 120.413, with correlation coefficients greater than r = 0.995. The low value of the RSD expressed the good repeatability and precision of the method. Experimental design and a response surface method were used to test robustness of the analytical procedure and to evaluate the effect of variation of the method parameters, namely the mobile phase composition, pH and temperature. They showed small deviations from the method setting. The good recovery and low RSD confirm the suitability of the proposed RP HPLC method for the routine determination of eletriptan hydrobromide and its impurity UK 120.413 in Relpax? tables.