The introduction of L-dopa (L-3,4-dihydroxyphenylalanine) therapy 40 years ago was a revolution in the treatment of patients with Parkinson s disease (PD). With time, however, the shortcomings of oral L-dopa medication became apparent, in particular the appearance of troublesome side effects, expressed as involuntary movements (dyskinesias) that developed over time in many patients. A gene therapy approach, aimed at restoring dopamine synthesis in the affected brain by viral vector delivery of genes that encode the dopamine-synthesizing enzymes, may offer a solution to this problem. Now, a team of French and UK researchers reports promising results in a nonhuman primate model of PD, paving the way for clinical trials of this enzyme-replacement approach.