Actigraphy measures physiological activity by using an acceleration sensor and RAM equipped with a data logger. Since actigraphy can continuously and easily record data over a long period of time without disturbing the normal activities of subjects, it is possible to analyze a large number of subjects. Actigraphy was performed in patients with Parkinson's disease who did not exhibit trembling. Results showed that the daily motor activity of patients was lower than that of the healthy individual. Daily motor activity was also found to be correlated with Hoehn-Yahr's classification. Furthermore, side-effects due to L-dopa, such as abnormal involuntary movement and on-off phenomenon, could be objective assessed. The results of long-term actigraphic examination, conducted after anti-Parkinsonian treatment, showed that akinesia improved with time. From these findings, it is concluded that actigraphy could quantitatively assess the degree of akinesia in Parkinsonian patients. Furthermore, actigraphy may be applied to the clinical assessment of drugs.