The aim of this study was to provide further insight into the phenomenology and pathophysiology of monophasic and biphasic dyskinesias induced by levodopa in Parkinson's disease. For this purpose, the type, localization, severity, and timing of dyskinesias were evaluated in 15 parkinsonian patients in relation to motor disability after administration of levodopa using a video-electromyographic recording device. Foot-dystonia, myoclonus, and akathisia were observed in most patients. The dyskinesias started in the foot, usually on the side most affected by the disease, and spread in an "ascending wave" to the contralateral side, the trunk, and upper extremities. In a few patients, onset was axial, spreading almost instantaneously to all limbs. The dyskinesias were dystonic and ballistic at the start, and became increasingly choreic as they attained the upper limbs. Their intensity was maximal in the lower limbs, then progressively decreased, while increasing in upper limbs and head. The results indicate that there is no strict dichotomy between biphasic and monophasic dyskinesias. In other words, there is a "continuum" between the first dyskinesias and those observed during the period of maximal clinical improvement. These dyskinesias can also appear in reverse order, as if there were an "oscillator" determining a sequence of alternating patterns.