Rats were trained to discriminate eltoprazine (1-(2,3-dihydro-1,4-benzodioxin-5-yl)-piperazine) (1.0 mg/kg p.o.) from demineralized water in a two lever operant procedure. Eltoprazine generalized to the 5-HT1B receptor agonist anpirtoline (6-chloro-2-[piperidyl-4-thiol]-pyridine hydrochloride), the 5-HT(1A,1B) receptor agonists batoprazine (8-(1-piperazinyl)-2H-1-benzopyran-2-one) and 1-NP (1-(1-naphthyl)piperazine hydrochloride), and to the 5-HT(1B/2C) receptor agonist mCPP (1-(3-chlorophenyl)piperazine dihydrochloride). The 5-HT1A receptor agonist flesinoxan (R(+)-N-[2[4-(2,3-dihydro-2-2-hydroxy-methyl-1,4-benzodioxin-5-yl) -1-piperazinyl]ethyl]-4-fluorobenzoamide) generalized partially and the 5-HT1A receptor antagonist WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride) failed to antagonize the eltoprazine cue, suggesting that 5-HT1A receptors are of limited importance in the discriminative stimulus properties of eltoprazine. Methiothepin, mCPP, mianserin and alprazolam did not antagonize the eltoprazine cue. The 5-HT(1A,1B,1D) receptor agonist GR46611X (3-[3-(2-dimethylamino-ethyl)-1H-indol-6-yl]-N-(4-methoxy-benzyl)acrylam ide) and the 5-HT(1B,1D) receptor antagonist GR127935T (N-[4-methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl) [1,1,-biphenyl]-4-carboxamide) did neither generalize to nor antagonize the eltoprazine cue, whereas (-)-alprenolol showed partial antagonism and substitution. These results show that the eltoprazine discriminative stimulus is mediated by the 5-HT1B receptor, although the lack of good 5-HT1B receptor antagonists weakens this conclusion.