Sixty patients with headaches of more than 15 days per month were recruited for this double-blind, placebo-controlled, parallel study of botulinum toxin type A (BTX) for chronic tension type and chronic migraine headaches. The primary efficacy point was the number of headache-free days as assessed by diary for 12 weeks after BTX injection. Secondary efficacy points included global impressions, the use of abortive headache medications, and palpation. After recruitment, subjects kept diaries for 4 weeks prior to randomization, at which time they received either 200 U of BTX or matching placebo and were followed. After the week-12 evaluation, patients were offered 200 U of BTX (open label), and were similarly followed for another 12 weeks. The mean days with headache of the 60 subjects (49 female, mean age 47 +/- 11 years) was 23 +/- 7 out of 30. Both groups were demographically similar (58 completed). Over a 12-week period after injections, headache-free days had improved in the BTX group from week 8 to 12 (P < 0.05), and strongly tended to improve over the entire 12-week period, 33 +/- 23 vs. 24 +/- 16 days without headache (P = 0.07), but did not meet the a priori significance criteria. The subject global impressions (P < 0.05), subject change in headache impressions (P < 0.005), and investigator global impressions (P < 0.001) all improved in the BTX group compared with placebo. Adverse events were mild and did not differ between groups. At week 24 (open label), headache-free days were less in the twice BTX injected group compared with the once injected group, 40 +/- 26 vs. 26 +/- 19 (P < 0.05). BTX may help chronic daily headache and appears to have a cumulative effect with subsequent injections. The treatment was very well tolerated.