Compounds having NR2B selective NMDA receptor antagonist activity are disclosed of the formula (I) ##STR00001## where two of the neighboring R.sup.1, R.sup.2, R.sup.3 and R.sup.4 groups form an imidazole ring fused to the benzene ring of the indole nucleus, and the other two of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 groups are hydrogen atoms, R.sup.5 and R.sup.6 together with the nitrogen between them form a saturated or unsaturated, 4-6 membered heterocyclic ring, which is substituted by phenoxy, phenyl-(C.sub.1-C.sub.4 alkyl), phenyl-(C.sub.1-C.sub.4 alkoxy), phenoxy-(C.sub.1-C.sub.4 alkyl), or benzoyl, optionally substituted on the aromatic ring by one or more halogen atoms, cyano or hydroxy groups, C.sub.1-C.sub.4 alkyl or C.sub.1-C.sub.4 alkoxy groups, X is NH--, Y is a --CH-- group, or pharmaceutically acceptable salts thereof formed with acids or bases.