Bromperidol, a new potent and long-acting neuroleptic of the butyrophenone series, and haloperidol were injected s.c. at the doses 0.01, 0.02, 0.04 and 0.08 mg/kg, in rats implanted with electrodes in the lateral hypothalamic region of the medial forebrain bundle. A dose-related response inhibition was found with both compounds and the graphically estimated ED50 value was 0.041 mg/kg for bromperidol and 0.047 mg/kg for haloperidol. These data are in complete agreement with our previous findings that bromperidol is a new potent and specific neuroleptic.