Objectives : To investigate the effects of (-)-3-PPP(0.5, 2, and 10mg/kg, s.c.) and haloperidol(0.1, 0.5, and 2mg/kg, s.c.) on the extracellular dopamine concentrations, and the effect of pretreatment with (-)-3-PPP(2mg/kg) on the haloperidol(2mg/kg)-induced extracellular dopamine concentrations in the nucleus accumbens(NAS) of free moving rats. Methods : Dopamine levels in dialysate were determined with high pressure liquid chromatography(HPLC) with electrochemical detection(ECD). Results : (1)(-)-3-PPP had dual actions depending on the doses: at 2mg/kg, it decreased and at 10mg/kg, increased extracellular dopamine concentrations ; (2) haloperidol at all doses increased dopamine levels with higher dose having a greater increase; and (3) pretreatment of (-)-3-PPP reduced the increase in dopamine levels elicited by acute treatment with haloperidol. Conclusions : These findings suggest that pretreatment of (-)-3-PPP in low dose could accelerate the onset of therapeutic effect of haloperidol by diminishing the haloperidol-induced dopamine release in the limbic system.