Several randomized, controlled studies have reported benefits of botulinum toxin type A (BoNTA; Allergan Inc., Irvine, CA, USA) over placebo in the treatment of migraine. Some studies reported significant benefits at dosages as low as 16 U, while other studies reported safety, tolerability, and efficacy at dosages up to 260 U. However, the optimal treatment paradigm and patient population have yet to be defined. To compare different injection sites and doses of BoNTA in the prevention of episodic migraine. This was a randomized, double-blind, placebo-controlled study of 232 patients with a history of four to eight moderate to severe migraines per month, with or without aura. Patients were randomized to placebo or one of four BoNTA groups that received injections into different muscle regions: frontal (10 U), temporal (6 U), glabellar (9 U), or all three areas (total dose 25 U). For 3 months following a single treatment, patients recorded migraine-related variables in a daily diary. BoNTA and placebo produced comparable decreases from baseline in the frequency of migraines (P > or = 0.411). In general, no statistically significant differences were observed for any efficacy variable. The overall rates of adverse events (any type) or treatment-related adverse events were similar among the groups. In this exploratory study of episodic migraine patients, low-dose injections of BoNTA into the frontal, temporal, and/or glabellar muscle regions were not more effective than placebo. BoNTA was safe and well tolerated. Future studies may examine higher BoNTA doses, flexible injection sites, multiple treatments, and disallow concomitant prophylactic medications.