BACKGROUND Previous open-label studies have demonstrated that botulinum toxin type B (BTX-B, Myobloc, Solstice Neurosciences) in doses of up to 3,000 U is safe and effective in the treatment of glabellar wrinkles. OBJECTIVE This double-blind, randomized, placebo-controlled, sequential-dose-escalation study evaluated the safety and tolerability of seven BTX-B doses ranging from 250 to 3,000 U in the treatment of subjects with hyperfunctional glabellar lines. METHODS Participants received a single intramuscular treatment of either BTX-B or placebo at five facial sites with a 12-week follow-up period. Primary efficacy outcome measure was the Investigator Global Scale score of subject's glabellar lines at rest and at full frown. Safety was evaluated primarily on the occurrence of adverse events (AEs). RESULTS The investigator scores demonstrated a statistically significant increasing dose-response trend in the percentage of subjects with no lines or mild lines at rest from Weeks 1 to 12 (p=.0420) and at full frown from Weeks 1 to 8 (p<.0001). Fifty-one subjects (36.7%) experienced AEs; the most common AE was headache not otherwise specified, experienced by 19 subjects (13.7%). CONCLUSIONS BTX-B at doses up to 3,000 U was safe and well tolerated in the treatment of hyperfunctional glabellar lines. Treatment with BTX-B reduced hyperfunctional glabellar lines in subjects, and the duration of action appeared to be related to the dose administered. Further studies using higher doses of BTX-B for treatment of glabellar wrinkles are planned.