From personal experience I’ve seen a Parkinson’s patient visibly stabilize after just a few minutes of Chi Kung. Regular Tai Chi training can only have an even stronger effect.

For Parkinson’s disease, exercise routines are often recommended to help maintain stability and the coordinated movements necessary for everyday living. An NIH-funded study, reported in the February 9, 2012 issue of the New England Journal of Medicine,* evaluated three different forms of exercise – resistance training, stretching, and tai chi – and found that tai chi led to the greatest overall improvements in balance and stability for patients with mild to moderate Parkinson’s disease.

Source: http://www.ninds.nih.gov/news_and_events/news_articles/Li_TaiChi_and_PD.htm