OBJECTIVE: The aim of this study was to assess the effectiveness of low- dose neuroleptic medication and monoamine oxidase inhibitor (MAOI) antidepressant medication in continuation pharmacotherapy of patients with borderline personality disorder. METHOD: The authors conducted a double-blind, placebo-controlled study comparing continuation therapy with a neuroleptic (up to 6 mg/day of haloperidol), an MAOI antidepressant (up to 90 mg/day of phenelzine), and placebo in 14 men and 40 women with borderline personality disorder. Continuation medication trials lasted 16 weeks, following 5 weeks of acute therapy. RESULTS: Continuing haloperidol demonstrated efficacy only for the treatment of irritability. Higher levels of depression, hypersomnia, and leaden paralysis were noted in the patients who received haloperidol than in those who received phenelzine and those who received placebo. The dropout rate during the first 8 weeks of the continuation study was significantly higher for the patients receiving haloperidol (64%) than for those receiving placebo (28%). Continued phenelzine demonstrated only modest efficacy for the treatment of depression and irritability. An activating effect of phenelzine was shown on measures of excitement and reactivity. CONCLUSIONS: No evidence of efficacy was found for continuation therapy with haloperidol in the treatment of borderline personality disorder other than in the treatment of irritability. Little evidence of efficacy was found for continuation therapy with phenelzine for borderline personality disorder other than modest improvements in irritability and depressive symptoms. There is currently no clear pharmacological treatment of choice for the continuation therapy of borderline personality disorder.