Postural instability has a big impact on the quality of life of patients with Parkinson's disease (PD) as it often leads to an insecure stance and fall. We investigated if postural stability in these patients improves by decreasing rigidity with a dopaminergic agonist. In our study, we tested eight PD patients with no concomitant diseases. Their age was 61 ± 2 years (mean ± SE) and their Hoehn-Yahr score was 3 ± 0.1. The patients were evaluated according to the Unified Parkinson's Disease Rating Scale for motor function (mUPDRS) and with stabilometric measurements of forward–backward and side-to-side body oscillations during free stance with eyes open. Both evaluations were performed in an ‘off’ state and in an apomorphine-induced ‘on’ state. As expected, the mUPDRS score was significantly decreased in the ‘on’ state with posture being improved in six patients, gait in eight patients and postural stability in seven of eight patients. In addition, apomorphine caused a significant reduction of the relative amplitude of lower frequencies and an increase of the relative amplitude of higher frequencies of forward–backward body oscillations. The results of stabilometry and mUPDRS evaluations are in agreement with the effect of apomorphine on rigidity, indicating that postural stability of PD patients is improved by decreasing rigidity.