Progressive loss of dopaminergic neurons in the substantia nigra pars compacta and the following reduction in striatal dopamine cause Parkinson's disease (PD). Transplantation of dopamine-producing cells into the striatum is a proposed treatment modality. In this report, we describe a model experiment assessing the effectiveness of mouse embryonic stem (ES) cell-derived dopaminergic neurons using a mouse model of PD. ES cells were shown to be an attractive and promising source for the generation of dopaminergic neurons, and the mouse PD model was useful to assess the efficacy of transplantation therapy with dopamine-producing cells, including ES cell-derived dopaminergic neurons.