Анотация: The objectives of this study were to evaluate the concentration of 8-alfa-hydroxymutilin (8alfa-HM) as marker residue for tiamulin (pleuromutilins group), to verify and validate an analytical method for the quantitative determination of 8-alpha-hydroxymutilin in porcine tissues (muscle and liver). Quantification of (8alfa-HM) was performed with liquid chromatography-tandem mass spectrometry (LC-MS/MS). This method was used to determine the residue of 8alfa-HM in porcine tissue after administration of Rodotet premix. In order to assess the residues in porcine tissues, an analytical method for 8-alpha-hydroxy-mutilin was verificated and validated in line with accordance of Commission Decision 2002/657/EC and VICH GL49