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We studied the effects—on parkinsonian signs, on levodopa‐induced dyskinesias, and on levodopa response—of acute experimental high‐frequency stimulation of the internal pallidum (GPi) during off‐drug and on‐drug phases. Thirteen quadripolar electrodes were evaluated in 8 patients with Parkinson's disease (PD). Stimulation of the most ventral contacts, lying at the ventral margin of or just below the GPi, led to pronounced improvement in rigidity and a complete arrest of levodopa‐induced dyskinesias. The antiakinetic effect of levodopa was also blocked and the patients became severely akinetic. Stimulation of the most dorsal contacts, lying at the dorsal border of the GPi or inside the external pallidum, usually led to the moderate improvement of off‐drug akinesia and could also induce dyskinesias in some patients. When using an intermediate contact for chronic stimulation, a good compromise between …