Summary: We report on three observations of parkinsonian patients with levodopa-induced diphasic dyskinesias, who received subcutaneous apomorphine to reduce the duration of abnormal movements. Apomorphine was effective in reducing the duration of diphasic dyskinesias at doses higher than the threshold doses necessary to induce an “on” phase (mean increase: 43%). However, after a few months of treatment, apomorphine was ineffective in stopping abnormal movements, even when doses were increased. In two patients, apomorphine remained effective in the morning, but increased the intensity of the dyskinesias in the afternoon. Acute diurnal variations of the pharmacodynamic striatal response are suggested explanation for these clinical observations.