The in vitro biological characterisation of the first potent and selective non-peptide neuropeptide Y Y-2 receptor antagonist, (S)-N-2-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6h)-oxodibenz[b,e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl] cylopentyl] acetyl-N-[2-[1,2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]-argininamid (BIIE0246) is reported. BIIE0246 displaced [I-125]neuropeptide Y with high affinity (IC50 = 3.3 nM) from the human neuropeptide Y Y-2 receptor and proved to be highly selective. BIIE0246 displayed antagonistic properties and thus represents the first selective non-peptide neuropeptide Y Y-2 receptor antagonist. (C) 1999 Elsevier Science B.V. All rights reserved.