Two sets of six samples of human serum spiked with predetermined concentrations of teicoplanin were circulated, 6 months apart, to 22 European laboratories for the purposes of external quality assessment (EQA). The laboratories returned assay results using either bioassay, high-performance liquid chromatography (HPLC) or fluorescence polarization immunoassay (FPIA). FPIA was the most popular method and performance was generally satisfactory. Some laboratories using HPLC or microbiological assay performed satisfactorily but others did not. Only seven laboratories (32%) showed consistently satisfactory performance. There appears to be a need for continuing EQA of clinical teicoplanin assays.