A fluorinated long-acting neuroleptic (fluphenazine decanoate) was detected in the human brain by fluorine nuclear magnetic resonance spectroscopy (MRS). The MRS system used had a 3 Tesla magnetic field, corresponding to a frequency of 118 MHz for the fluorine nucleus (Bruker Medspec 3 Tesla, 60-cm magnet bore width). The spectra were obtained with a surface coil having a 10-cm diameter, which was centered alternatively on the frontal lobe and basal ganglia, and on the occipital lobe. The impregnation and elimination kinetics of fluphenazine were monitored during three sessions (4 hours, 5 days, and 11 days after injection of the compound). This technique can be usefully applied to the in vivo study of the pharmacokinetics and site of action of psychiatric compounds in man.