Relying on recent experimental data in 2 animal models of Parkinson disease (PD), we have tested the effects of the loop diuretic bumetanide as an add-on treatment to dopaminergic drugs in 4 volunteered patients with PD using the Unified Parkinson's Disease Rating Scale. Bumetanide is a specific antagonist of the chloride importer NKCC1 (sodium/potassium/chloride cotransporter isoform 1) that ameliorates neuronal inhibition by reducing intracellular chloride levels in a variety of pathological conditions. Bumetanide is however not labeled for use in PD. We report an improvement of PD motor symptoms in the 4 patients treated with bumetanide (5 mg/d for 2 months). Bumetanide also improved gait and freezing in 2 of these patients. Our results suggest that bumetanide is well tolerated and call for double-blind, placebo-controlled, randomized trials to confirm the therapeutic efficacy of bumetanide.