GM1 ganglioside (GM1) has in the past been reported to promote regenerative sprouting and functional recovery in both central and peripheral nervous systems. The present experiments were performed in order to investigate whether GM1 might have any therapeutic effect on young mice who had been exposed to the Parkinson-producing neurotoxin MPTP. GM1 caused moderate to dramatic increases in striatal dopamine levels, depending upon duration of exposure to GM1, in animals previously exposed to MPTP. Furthermore, the effects of GM1 on enhancing striatal dopamine levels were apparent when GM1 administration was delayed until 3 days after the last MPTP injection was given and these effects were not reversed when GM1 was withdrawn. Tyrosine hydroxylase (TH) immunohistochemistry of the striatum demonstrated increased numbers of TH-positive fibers and TH-positive terminal fields in GM1-treated animals as compared to animals that received only MPTP. TH immunohistochemistry of the substantia nigra revealed little or no loss of parts compacta neurons in the MPTP-treated mice. On the basis of these observations, GM1 appears to increase the dopamine content of the striatum by promoting or stimulating regenerative sprouting of dopaminergic terminals and perhaps collateral sprouting from remaining intact fibers in the MPTP model of Parkinsonism in the young mouse. We suggest that GM1 ganglioside may hold some promise as a potential adjunct in the treatment of Parkinson's Disease.