Abstract <p>A selective procedure was developed for the determination of 20 beta agonists in muscle tissue and liver using chromatography–mass spectrometry. The limit of quantification of the procedure is 0.1−0.25 (0.5) μg/kg (depending on the compound to be determined). The procedure is based on the hydrolysis of test materials with the subsequent extraction of the analytes with acetonitrile acetate, obtaining an organic fraction by salting out, purifying it on a layer of aluminum oxide, dispersive purification with C₁₈, and final purification by liquid–liquid extraction with hexane. Data on promising ion transitions of some analytes were presented, and the detection parameters for bambuterol, formoterol, and phenylethanolamine A were established. Data on optimization of the processes of hydrolysis, extraction, and purification of the extracts were reported. Information on step-by-step analyte losses was given, and data on the analysis of reference materials were obtained. The validation of the procedure developed showed that the relative expanded uncertainty varied in a range from 7 to 24%.</p>