Polymyographic recordings were used to identify the most dystonic muscles suitable for local injection with botulinum toxin in 100 patients with spasmodic torticollis (TS). Rotating TS (72% of the patients) was due to dystonic activity of the splenius muscle ipsilateral to and/or the sternocleidomastoid muscle contralateral to the side of chin deviation. One-third of these patients had also dystonic activation of the contralateral splenius muscle and, rarely, the contralateral trapezius muscle. Ten patients had laterocollis due to dystonic activation of all recorded muscles on one side of the neck. Nine patients had retrocollis due to activity of both splenius muscles and rarely additional activity in both trapezius muscles. The type of dystonic muscle activity was found to be tonic, phasic or tremulous. Besides the evaluation of spontaneous dystonic EMG activity further examination during the "geste antagoniste" or the muscle activity during rotating head movements can provide additional information. It is concluded that polymyography may provide a rationale for identifying the dystonic muscles underlying the different forms of TS. It may prove to be helpful for the successful therapy with botulinum toxin and may be useful in differentiating tremulous torticollis from other types of head tremor.