Neuroprotective therapy for Parkinson's disease (PD) is a treatment intended to prevent or reduce neuronal degeneration. Since clinical studies to evaluate such an effect would be prolonged, the choice of agents for use as possible neuroprotective therapy is based on the results of in vitro and animal experiments. Free radicals are currently regarded as the most important factor in the progression of PD. One current possible neuroprotective therapy is reduction of levodopa dose, since levodopa is a source of free radical formation. Dopamine (DA) metabolism inhibition, and administration of the DA agonist bromocriptine that eliminates hydroxyl free radicals have neuroprotective effects experimentally. The other candidates for neuroprotective agents are still under development. However, those whose clinical use is permitted should be considered for use, since patients with long-standing PD cannot wait until the neuroprotective efficacy of these agents is confirmed by clinical study.