“The development of antibiotic resistance in bacteria has been attributed to the use of antimicrobials in human medicine. The contributions of veterinary medicine and agriculture to antibiotic resistance are still being investigated.”1 Hence, there is pressure on analytical scientists to detect and confirm the presence of antimicrobials in foods of animal origin. The aminoglycosides and macrolides are two families of antibiotics that are very similar in structure and have important applications in veterinary medicine. These antibiotics are widely used in the treatment of bacterial infections e.g. aminoglycosides for enteritis and mastisis and macrolides for enteric infections. They have also been used as feed additives for growth promoting. As a result, legislation has been laid down by the European commission in which member states must meet strict criteria for monitoring these residues. This thesis was undertaken to develop a UPLC-MS/MS method for the simultaneous analysis of the aminoglycoside and macrolide antibiotics. This is the first time that a combination method for the two classes of compound was developed. A Waters Acquity/ Premier XE system with a dual ESI/APCI probe allowed for optimisation of detection for each component within a single run. For all target compounds the optimum MS ionisation mode and conditions were determined experimentally. The chromatographic conditions were investigated in order to improve separation, reduce analytical run times and meet validation requirements as per Commission Decision 2002/657/EC. While the scope of this thesis did not allow for the method to be expanded to cover the many sample matrices/ species that are required by the EU it is hoped that this will be investigated in the future. This thesis did however contain a comprehensive literature review of the current techniques employed to analyse for these residues both qualitatively and quantitatively. Sample preparation was researched and an extraction experiment was carried out comparing various solid phase extraction columns and discussed in detail in chapter 2. This experiment looked at various extraction methods to minimise matrix effects and optimise recoveries. Finally, the novel method developed and optimised for the analysis of the macrolide and aminoglycoside antibiotics using UPLC-MS/MS is presented. This will be applied to the analysis of real samples in the Central Meat Control laboratory which is a National Reference Laboratory (NRL) and expanded to cover the many species required for e.g. bovine, ovine and porcine tissues.