In vivo 19F NMR measurements of the fluorinated neuroleptic melperone [4'-fluoro-4-(4-methylpiperidino)-butyrophenone hydrochloride] in the rat brain were performed using a geometrically optimized surface coil at 4.7 T. It was possible for the first time to detect a signal of a monofluorinated neuroleptic drug with a time resolution of 30 min after i.p. application. The kinetic time course of the investigated neuroleptic melperone was recorded over 6 h and showed that the half-life in the rat brain is 4.3 h. The total amount of drug and its metabolites in the brain was estimated to be 50 microM. the chemical shift of the 19F NMR signal shows the same upfield shift relative to that in aqueous solution as has been reported for trifluorinated neuroleptic drugs.