Objective To induce significant improvement of motor abnormalities and striatal dopamine (DA) levels in rat model of Parkinson's disease (PD), by intracerebral grafting of the genetically modified muscle cells expressing tyrosine hydroxylase (TH).Methods Primary myoblasts and myotubes from the rat were prepared by cell culture and a plasmid, pCMVTH,containing TH gene and a promoter of cytomegalovirus (CMV) was constructed by DNA recombination technique. The primary muscle cells were transfected with newly constructed pCMVTH DNA vector, by using lipofection. These genetically modified muscle cells were grafted into the caudate- putamen of 6-OHDA-lesioned rats, representing PD models. Before and after grafting, the rotational behaviour and the striatal levels of DA and its metabolities were tested at different postoperative survival times. In addition, the immunocytochemistry for showing TH activity was done both in vitro and in vivo.Results The newly constrcuted plasmid, pCMVTH was proved to contain TH gene and have correct direction of insertion. The cultured primary myoblasts and myotubes lipofected with pCMVTH were immunocytochemically shown to express TH activity in vitro. After grafting, these TH-expressing muscle cells showed to have a long-term survival cells in vivo and induced a marked decrease in abnormal locomotion and a increase in striatal DA levels for PD rat model.Conclusions In experimental gene therapy for PD, the pCMVTH is a useful vector for carrying TH gene. The lipofection is a practical technique for transferring a target gene into eukaryotes and primary cultured muscle cells should be a good vehicle for DNA transfer and intracerebral grafting.