Nonenzymatic FeCl2-catalyzed oxidation of methotrimeprazine (levomepromazine) yielded three ring-hydroxylated derivatives that had different GC retention times but almost identical mass spectra. Two of these, together with O-desmethylmethotrimeprazine, were identified by combined GC/MS in enzymatically hydrolyzed urine from four psychiatric patients, who had been treated with oral doses of methotrimeprazine. The mass chromatograms indicated that the three metabolites were formed in similar amounts. Small amounts of three other metabolites were also found in the urine after enzymatic hydrolysis. These were identified as O-desmethyl-N-monodesmethylmethotrimeprazine and two monohydroxy-N-monodesmethyl derivatives that had different GC retention times. None of those metabolites were found in unconjugated form in the urine.