A chromatographic method for quantifying the potential antipsychotic compound BIMG 80 (I) was developed and employed for plasma and brain measurements in rats given pharmacologically effective (ED50) doses in the dexamphetamine-antagonism test. The analytical procedure is based on isolation of the compound and the internal standard (haloperidol) from plasma and brain constituents using the LC-18 SPE cartridge, with satisfactory recovery and specificity, isocratic separation on a C18 reversed-phase column coupled with a UV detector set to 225 nm.