Fluorine-19 (F-19) is a nonradioactive isotope that is well-suited to nuclear magnetic resonance spectroscopy (NMRS) and is a constituent of several medications used to treat psychiatric illnesses. Fluoxetine, a trifluorinated agent, generated a signal from brain that was readily measured by F-19-NMRS. Estimated brain concentrations ranged from 1.3-5.7 mug/ml in six subjects at a steady state dose of 40 mg/day. Enhanced sensitivity of F-19 has been obtained by conforming the surface coil to the shape of the forehead. Hence. at the current state of development, F-19-NMRS can be applied to clinical questions relevant to concentrations of fluoxetine in brain, We also report observation of NMRS signals from fluorinated neuroleptics in a number of patients at steady state. These signals continue to be difficult to obtain, although a correlation between dose and estimated brain concentrations is suggested.