Because of conflicting reports of the actions of the antiparkinsonian agent L-prolyl-L-leucyl-glycine amide (PLG, MIF-I) on the turnover of Striatal dopamine (DA), this process was reinvestigated. In the present series of studies, it was found that neither our MIF-I (200 ng ICV) nor the MIF-I used by Versteeg et al. [25]was effective in altering the rate of decline of endogenous DA in the caudate nucleus of rats pretreated with α-methyl-p-tyrosine (300 mg/kg IP). In addition, our MIF-I (1 mg/kg IP) did not change endogenous dihydroxyphenylacetic acid (DOPAC) or homovanillic acid (HVA) in rat striatum. These studies indicate that MIF-I does not alter the turnover rate of DA in nigrostriatal neurons. It is possible that MIF-I or some substance released by MIF-I acts at a posfsynaptic receptor site.