Zolmitriptan is a selective 5-HT1B/1D receptor agonist for acute oral migraine therapy. This randomized, placebo-controlled, parallel-group study investigated the efficacy and tolerability of oral zolmitriptan (5, 10, 15 and 20 mg) in the treatment of single acute migraine attacks. Of 1181 patients randomized, 840 were evaluable for the primary efficacy analysis. Headache response rates (a reduction in headache intensity from severe or moderate at baseline to mild or no pain at 2 hours post-treatment) were similar across the zolmitriptan dose groups (66%, 71%, 69% and 77% for 5 mg, 10 mg, 15 mg and 20 mg, respectively) and were significantly higher than that for placebo (19%; all groups P < 0.001). A headache response was reported at 1 hour by 40-50% of zolmitriptan recipients (16% placebo). At 2 hours post dose, 39-47% of zolmitriptan-treated patients were pain-free, compared with 1% of placebo recipients. Headache recurrence occurred in 21-29% (upper 95% CI 37.1) of zolmitriptan-treated patients and in 65% (95% CI 38.3, 85.8) of placebo recipients. Zolmitriptan was well tolerated at each dose. The most commonly reported adverse events were asthenia, dizziness, paraesthesia and feelings of heaviness. Most adverse events were of mild or moderate intensity and were transient. The frequency of adverse events was dose-related. Although, zolmitriptan 5 mg exhibited the most favourable efficacy and tolerability profile, the dose response data suggest that lower doses would also offer significant efficacy. Copyright 1998 Lippincott Williams & Wilkins