To investigate whether preprogramming (Bereitschaftspotential, BP) and control activity (skilled performance positivity, SPP) in a complex task are sensitive to L-dopa, movement related potentials (MRPs) were recorded in 12 non-demented Parkinson's disease (PD) patients before and after acute L-dopa administration, and in 17 control subjects. After L-dopa administration, the PD patients scored a significantly higher percentage of correct performances ( p<0.05), linked to a decreased BP amplitude ( p<0.001) and an increased SPP amplitude ( p<0.005), than before therapy. Our findings suggest that preprogramming activity is impaired in untreated PD patients. Dopaminergic drug administration seems to restore their ability to use more automatic motor strategies which become more similar to that of normal subjects.