Naphyrone (1-naphthalen-2-yl-2-pyrrolidin-1-yl-pentan-1-one; naphthylpyrovalerone, β-naphyrone) is a cathinone designer drug and was marketed as replacement for the synthetic cathinone derivative mephedrone. Meanwhile, naphyrone is also classified as a controlled drug in several countries. Therefore, the aim of this study was to identify the metabolites of naphyrone in rat urine using gas chromatography-mass spectrometry techniques and to show its detectability in urine samples. The following metabolic steps could be detected in rat urine: oxidation of the pyrrolidine ring to the corresponding lactam, hydroxylation of the propyl side chain and the naphthyl ring, degradation to the primary amines after opening of the pyrrolidine ring, and combinations of these steps. Assuming similar kinetics, an intake of naphyrone should be detectable in human urine mainly via its metabolites. Copyright © 2013 John Wiley & Sons, Ltd.