Isolates from four UK centres, comprising four Staphylococcus aureus strains and one Staphylococcus epidermidis strain with high-level mupirocin resistance, and one strain each of Staphylococcus aureus and Staphylococcus epidermidis with low-level mupirocin resistance, were assessed for intracellular or extracellular enzymatic alteration of the antibiotic. No change was seen in a number of assays, which included comparative disk diffusion, well diffusion and high-pressure liquid chromatography. Other mechanisms of resistance need to be explored in these isolates.