Objective To induce significant improvement of motor abnormalitie s and striatal dopamine (DA) levels in rat model of Parkinson's disea se (PD), by intrac2 erebral grafting of the genetically modified muscle cells expressing tyro sine hydroxyla se (TH). Me t h o ds Primary myobla st s and myotube s from the rat were prepared by cell culture and a plasmid, pCMVTH, containing TH gene and a promoter of cytomegalovirus (CMV) wa s constructed by DNA recombination technique. The primary muscle cells were transfected with newly constructed pCMVTH DNA vector, by using lipofection. The se genetically modified muscle cells were grafted into the caudate-putamen of 62OHDA2le sionedrats, repre senting PD models. Before and after grafting, the rotational behaviour and the striatal levels of DA and it s metabolitie s were te sted at different po stoperative survival time s. In addition, the immunocy to chemistry for showing TH activity wa s done both in vitro and in vivo. Results The newly constrcuted pla smid, pCMVTH wa s proved to contain TH gene and have correct direction of insertion. The cultured primary myobla st s and myotube s lipofected with pCMVTH were immunocytochemically shown to expre ss TH activity in vitro. After grafting, the se TH2expre ssing muscle cells showed to have a long2term survival cells in vivo and induced a marked decrea se in abnormal locomotion and a increa se 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 eukaryote s and primary cultured muscle cells should be a good vehicle for DNA transfer and intracerebral grafting.