A 37-year-old man had a considerable concentration of methamphetamine in his urine, but he denied taking any abused drug. It was found that he took a pain killer that contains famprofazone, a relatively strong analgesic whose metabolites include methamphetamine and amphetamine. The human urinary metabolism of famprofazone was investigated. Immunoassay was used as a preliminary test, and gas chromatography with flame-ionization detection and gas chromatography-mass spectrometry were used for quantitation and confirmation.