We reported previously the protective effect of 17β-estradiol (17β-E2) on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopamine (DA) depletion. This protection was stereospecific, because 17β-E2 showed activity but 17α-estradiol (17α-E2) did not. The mechanisms by which estradiol exerts its beneficial effects, however, remain unknown. We investigated a possible implication of enkephalins (ENK) in neuroprotective activity of 17β-E2. Protection against MPTP-induced DA depletion was obtained with 17β-E2 but not 17α-E2. MPTP lesion increased striatal preproenkephalin (PPE) mRNA levels and they remained elevated in 17α-E2-treated MPTP mice whereas 17β-E2 treatment decreased these levels to control values. This is the first report of estradiol modulation of striatal PPE mRNA in mice. Negative and significant correlations between DA levels, vesicular monoamine transporter (VMAT2) density, and PPE mRNA were observed in the striatum of lesioned animals. This effect of 17β-E2 on PPE mRNA after a lesion could be one of many mechanisms by which this steroid exerts its neuroprotective activity. © 2005 Wiley-Liss, Inc.