BACKGROUND: Different formulations of botulinum toxin type A can behave differently. There has been little clinical research directly comparing formulations. OBJECTIVE: We sought to compare the efficacy and tolerability of two botulinum toxin type A formulations-BoNTA1 and BoNTA2-in the treatment of moderate and severe glabellar lines. METHODS: Sixty-two patients with moderate or severe glabellar lines at maximum contraction were randomly assigned to receive 20 U of BoNTA1 or 50 U of BoNTA2 (20% in the procerus muscle, 80% in the corrugator muscles). RESULTS: The incidence of 1-grade improvement or greater in glabellar line severity at maximum contraction was as follows: 77% (BoNTA1) versus 59% (BoNTA2) at week 12, 53% versus 28% at week 16. The estimated incidence of relapse was 23% (BoNTA1) versus 40% (BoNTA2) at week 16. Both formulations were similarly well tolerated. LIMITATIONS: Few male and non-Caucasian subjects were studied. CONCLUSION: BoNTA(1) offered more prolonged efficacy than BoNTA2 in the treatment of glabellar lines at the dose ratio of 2.5:1 (BoNTA2:BoNTA1) used in this study.