The behavioral and neurochemical effects of switching from typical to atypical medications have not been evaluated in the rodent models of tardive dyskinesia. Thus, we treated rats with haloperidol-decanoate for 12 weeks, and assessed the effects of additional treatment with olanzapine, haloperidol, clozapine, or vehicle on vacuous chewing movements and expression of transcripts for dopamine receptors, tyrosine hydroxylase, δ-opioid receptor, prodynorphin, preproenkephalin, glutamic acid decarboxylase-65 (glutamic acid decarboxylase (GAD)-65) and GAD-67 and N-methyl-D-aspartate (NMDA) receptor subunits in the striatum and its efferent pathways. Haloperidol-decanoate induced vacuous chewing movements extinguished following an additional 4 weeks of treatment with vehicle, olanzapine or haloperidol, but not clozapine. Post-treatment, vacuous chewing movements in the clozapine group were significantly higher than the vehicle, olanzapine and haloperidol groups. GAD-67 mRNA expression in the globus pallidus was decreased following additional treatment with olanzapine or haloperidol, but not clozapine. Changes in expression of other transcripts were not detected. These findings demonstrate important differences in the effects of typical and atypical antipsychotics on chronic vacuous chewing movements. © 2003 Elsevier B.V. All rights reserved.