The preliminary report for the proficiency test STRD0521 is now available on the FIS-VL. The objective of this proficiency test was to allow the participants to assess the performance of their routine methods for the analysis of nitroimidazoles in plasma. Additionally, a milk sample was supplied, which participants were asked to analyse using their routine method for the analysis of milk, or, if no such method was available, their analytical method for plasma. All participants are asked to have a look at their results and communicate any deviations from the results they submitted to the EURL Berlin by 15 December 2021.