An HPLC method of determination of lasalocid was developed for fast monitoring of its content as an undesirable additive in final fodders. Lasalocid is extracted from a sample with a mixed solvent ethyl acetate - hexane and, after purification of the extract with silica gel, it is determined by HPLC on a reverse C₁₈ phase with fluorescence detection. The determination limit (50 µg/kg), repeatability (0.1 mg/kg) and yield of the method (95 %) were found for lasalocid concentrations 0.5-5 mg/kg. The repeatability was determined for real samples of final fodders.