The reproducibility of plasma protein quantitation between laboratories and between instrument types was examined in a large-scale international study involving 16 laboratories and 19 LC–MS/MS platforms, using two kits designed to evaluate instrument performance and one kit designed to evaluate the entire bottom-up workflow. There was little effect of instrument type on the quality of the results, demonstrating the robustness of LC/MRM-MS with isotopically labeled standards. Technician skill was a factor, as errors in sample preparation and sub-optimal LC–MS performance were evident. This highlights Please cite this article in press as: A.J. Percy, et al., Inter-laboratory evaluation of instrument platforms and experimental workflows for quantitative accuracy and reproducibility assessment, EuPA Open Proteomics (2015), http://dx.