The isotopic composition of ozone depleting methyl halides may provide valuable information on the sources and sinks of these compounds. However, so far mostly stable carbon isotope analysis of methyl chloride and methyl bromide has been at­tempted. One obstacle to progress with their other isotope systems has been the challenge to obtain sufficiently large amounts of methyl halides to meet the detection limits of existing isotope analytical methods. A compound-specific technique using gas chromatography multiple-collector inductively-coupled plasma mass spectrometry (GC-MC-ICPMS) has in this work been developed to measure ⁸¹Br/⁷⁹Br isotope ratios in CH₃Br. This ICPMS method is three orders of magnitude more sensitive compared to existing gas source mass spectrometry methods (dual inlet and continuous flow) for Br isotope determination and thus opens up possibilities for applications toward ambient atmospheric samples to investigate the sources and sinks of methyl halides.