In vivo naked DNA gene transfer method was used in gene therapy of Parkinson's disease (PD). The complex of rat tyrosine hydroxy-lase (TH) expression plasmid and Lipofectin was injected stereotaxically into striatum of PD rat model. The asymmetric rotational behavior was reduced substantially and quickly. On the third day after injection, drug-induced rotation decreased 50% compared with pretreatment scores. Immunohistochemical staining showed TH-positive nerve cells in striatum of injection side, which indicated that TH gene was uptaked and expressed by nerve cells. These preliminary results have general implications for the application of naked DNA transfer techpique in gene therapy of human neurological disease and specific implications for PD.