A (substituted-aralkyl)heterocyclic compound of the formula I wherein R1 is an azido, carbamoyl, cyano, formyl, hy-droxy or nitro radical, a 1-6C 1-hydroxyalkyl, alkoxy, alkylcarbamoyl, alkylthio, alkylsulphinyl or alkylsulphonyl radical, a 2-cyanoethyl radical, optionally bearing one to four 1-6C alkyl substituents, or a 2-6C alkanoyl, halogenoalkanoyl, alkanoyloxy, alkanoylamino, dialkylcarbamoyl or alkoxycarbonyl radical; R2 and R3, which may be the same or different, are each a hydrogen atom, a 1-6C alkyl, dueterioalkyl or halogenoalkyl radical, or a phenyl or phenyl(l-6C alkyl) radical, in each of which the phenyl may optionally bear one or more substituents; or R2 and R3, together with the carbon atom to which they are attached, may form a 3- to 6-membered ring; or R1R2R3C- is a 1,1-dicyanoethyl or trifluoromethylsulphonyl radical; R4 is a hydrogen or halogen atom, a cyano or nitro radical or a 1-6C alkyl or halogenoalkyl radical; R5 has any of the values de-fined above for the group RIR2R3C but is not necessarily the same as R1R2R3C, or has any of the values de-fined above for R4 but is not necessarily the same as R4, or is a carbamoyl, 1-pyrrolidinyl-carbonyl, piperidino-carbonyl, morpholinocarbonyl or nitro radical, a 1-6C alkoxy or halogenoalkoxy radical or a 2-6C alkanoyl or alkoxy-carbonyl radical; A is a methylene or ethylene radical optionally bearing one or more substituents selected from deuterium and halogen atoms, carbamoyl, cyano and hydroxy radicals, 1-6C alkyl and alkoxy radicals, and 2-6C alkanoyloxy radicals provided that when A is linked to R through a nitrogen atom thereof, it may not bear a hydroxy, alkoxy or alkanoyloxy sub-stituent on the carbon atom adjacent to such nitrogen atoms; and R6is a lH-l,2,4-triazol-l-yl, 4H-l,2,4-triazol-4-yl, IH-imidazol-1-yl, 5-cyano-lH-imidazol-l-yl, 3-pyridyl or 5-pyrimidinyl radical, or a IH-imidazol-1-yl radical, bearing at the 5-position thereof a 1-6C alkyl substituent which is itself optionally substituted by one or more carbamoyl, cyano, hydroxy or 2-6C alkoxycar-bonyl radicals; and provided that when R2, R3, R4 and R5 are hydrogen, A is a methylene radical and R6 is a 3-pyridyl radical, R1 is not a cyano, hydroxy or hydroxymethyl radical, and when R1 is a hydroxy radical, R3, R4 and R5 are hydrogen, A is a methylene radical and R6 is 3-pyridyl, R2 is not a methyl or a 2-chloro-1-methylethyl radical, and provided that when R1 is a methoxycarbonyl radical, R2, R3, R4 and R5 are hydrogen and A is a methylene radical, Ri is not a IH-imidazol-a1-yl radical; and the pharmaceutically acceptable acid addition salts thereof