In order to check the specificity of a radioimmunological assay for haloperidol and bromperidol reported by Michiels et al. (1) and commercialized by IRE (Fleurus, Belgium), the assay was performed on canine and human plasma samples with and without extraction. After a single dose of bromperidol in dogs, plasma levels obtained with and without extraction were similar. In man the plasma levels for bromperidol after a single administration were markedly lower after extraction. The same was true for haloperidol plasma levels after chronic dosing in man. The findings suggest that the direct radioimmunoassay of haloperidol or bromperidol with the commercialized kit, lacks specificity of humans, possibly because of the presence of one or more polar metabolites.