Objective To examine whether tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) genes can be cotransduced into the same target striatal cells using adeno-associated virus (AAV) vectors, and to determine whether the cotransduction would result in better biochemical change than the TH gene alone.Methods TH and AADC genes were cotransduced into cultured striatal cells with separate AAV vectors. Expressions of TH and AADC were detected by immunocytochemistry; intracellular catecholamine levels were assayed by high-performance liquid chromatography (HPLC).Results TH and AADC genes were efficiently cotransduced into the striatal cells. Specifically, the coexpression of TH and AADC resulted in more effective dopamine production compared with the TH gene alone.Conclusion Using AAV vectors, coexpression of TH and AADC in the striatal cells might be a useful approach to gene therapy for Parkinson's disease.