The treatment with neuroleptic drugs, such as the butyrophenones, has been based on clinical empiricism, rather than on pharmacokinetic knowledge or on a clear understanding of the mode of action of the drugs. To obtain pharmacokinetic data a specific and sensitive analytical method is necessary. The determination of butyrophenones in a biological medium poses many analytical problems, due to the low dose of these drugs. Very recently Forsman published a pharmacokinetic study of haloperidol in man by electron capture detection. No such study is available for bromperidol. In our paper, we will present comparative data for the quantitative determination of bromperidol by mass fragmentography, gas chromatography with electron capture detection, and radioimmunoassay. Our results show that for the determination of bromperidol in plasma, only radioimmunoassay is sensitive enough to allow the easy determination of the low plasma levels to be expected for bromperidol.