A class of chemical compounds comprising a pyrrolo[2,3-b]pyridine moiety and a halo-substituted heterocyclic moiety, linked via the 3-position of the pyrrolo[2,3-b]pyridine moiety by a methylene group, are ligands for dopamine receptor subtypes within the body and are therefore useful in the treatment and/or prevention of disorders of the dopamine system, in particular schizophrenia.