Botulinum toxin injections were given to 23 patients with cervical dystonia in a double-blind, placebo-controlled, crossover study. Each patient was randomly given 100 units of botulinum A toxin and placebo in two respective sets of injections into the two most active contracting neck muscles at least 3 months apart. Before and 3 weeks after each set of injections, the cervical dystonia was "blindly" scored by the investigator. Each patient was also asked to independently score the improvement of the dystonia and neck pain. Four patients dropped out and one patient showed spontaneous remission. The remaining 18 patients completed the study and showed a significant improvement after the injections of botulinum toxin in comparison with that of the placebo. The effect started about 1 week after injection and the maximal effect lasted about 11 weeks in patients with a satisfactory response. The neck pain was satisfactorily relieved in 9 of 10 patients affected. There were no significant side effects. Thus, botulinum toxin injection is effective in treating cervical dystonias; injection of a higher dose of botulinum toxin in a greater number of neck muscles is required for those patients with complex cervical dystonia.