The invention concerns N-oxides of certain pyridylmethylpiperazine and -piperidine derivatives as alternatives or as `prodrugs' of their respective parent compounds, to pharmaceutical compositions containing these N-oxides, to methods for preparing them, and methods for preparing compositions. The invention relates to N-oxides of compounds having formula (a), wherein the symbols have the meanings given in the description, and wherein the oxidized nitrogen atom may be the nitrogen atom in the pyridyl ring of R<；SUB>；5<；/SUB>；, or the nitrogen atom in the piperidine ring (when Z is carbon) or either one of the nitrogen atoms in the piperazine ring (when Z is nitrogen), or bóth the nitrogen atom connected to R<；SUB>；5<；/SUB>； via a methylene group, ánd the nitrogen atom in the pyridyl ring of R<；SUB>；5<；/SUB>；, and tautomers, stereoisomers, pharmacologically acceptable salts, hydrates and solvates thereof. The invention also relates to the uses of such N-oxides and compositions, particularly for the manufacture of a medicament useful in the treatment of affections or diseases of the central nervous system caused by disturbances in either the dopaminergic or serotinergic systems, for example Parkinson's disease, aggression, anxiety disorders, autism, vertigo, depression, disturbances of cognition or memory and in particular schizophrenia and other psychotic disorders.L'invention concerne des N-oxydes de certains dérivés de pyridylméthylpipérazine et -pipéridine en tant qu'alternatives ou en tant que « promédicaments » de leurs composés parents respectifs, des compositions pharmaceutiques contenant ces N-oxydes, leurs procédés de préparation et des procédés de préparation des compositions. L'invention concerne des N-oxydes de composés de formule (a), dans laquelle les symboles ont les significations données dans la description et dans laquelle l'atome d'azote oxydé peut être l'atome d'azote du cycle pyridyle de R5 ou l'atome d'azote du cycle pipér
