We recently reported that some patients with borderline personality disorder (BPD) exhibit a blunted thyrotropin (thyroid-stimulating hormone; TSH) response to thyrotropin-releasing hormone (TRH). Because it is known that dopamine can inhibit the TSH response to TRH and that some patients with BPD show improvement with antipsychotic (dopamine-blocking) medication, we investigated whether haloperidol could reverse the blunted TSH response in BPD. Of 12 patients with BPD, three showed a blunted TSH response that did not normalize with haloperidol. Furthermore, there were no overall group changes in TSH response with haloperidol. The present study suggests that reductions in TSH response in BPD are not secondary to dopamine.