[en] Serial PET studies of N-[¹¹C]methylspiroperidol and [¹⁸F]N-methylspiroperidol were carried out in a single baboon with an intervening time period of 2 h between injection of the ¹¹C and the ¹⁸F-labeled tracers. The kinetic patterns of uptake and egress of radioactivity in striatum and cerebellum as well as the magnitude of the uptake was very similar with the two tracers. No significant difference in clearance of total radioactivity from arterial plasma was detected. Analysis of plasma radioactivity for unchanged drug showed no significant differences in the amount of unchanged tracer at different times, although the profile of labeled metabolites was different. These results indicate that the only significant difference between the use of N-[¹¹C]methylspiroperidol and [¹⁸F]N-methylspiroperidol for PET studies of brain dopamine receptors relate to the difference in physical half-life of the radionuclide rather than to differences in the profile of metabolically produced labeled compounds. (author)