A clinical trial was undertaken to evaluate the effects of commercially available botulinum toxin on 14 hyperactive corrugator muscles, 14 procerus muscles, one case of congenital aplasia of the depressor labii inferioris muscle, and one case of iatrogenic injury to the ramus mandibularis branch of the facial nerve with paralysis of the depressor labii and mentalis muscles. Of the 31 muscles injected, 28 were appropriately paralyzed with the initial injection. The desired results were obtained in the 3 remaining muscles following a second injection. The ability to frown was nullified in all subjects, resulting in the elimination of glabellar lines. Facial symmetry was achieved in both patients with muscle imbalance. The average duration of the paralysis was 8 weeks, with a range of 2 to 16 weeks. However, this period was prolonged in the latter part of the study with an adjustment of the toxin dose. Our results demonstrate that botulinum toxin injected into overactive facial muscles does produce a predictable and reversible paralysis and eliminates or ameliorates deep frown lines. We also illustrate its use in achieving facial symmetry in one patient with congenitally absent depressor labii inferioris and platysma muscles and in another with postrhytidectomy facial nerve paralysis.