To investigate prospectively serious adverse events associated with sumatriptan injection, we studied 12,339 typical migraineurs for up to 12 months each. This study imitated the ordinary clinical use of sumatriptan injection except that: (a) a short, written informed consent was required, (b) there was a centralized, automated dispensing service that audited each patient's product use, (c) patients were sometimes reviewed by telephone, and (d) drug supply and medical consultation were without charge. All adverse events were recorded regardless of etiology. There were 25 fatalities during the study, none being attributable to sumatriptan injection. Of six strokes in the study, two occurred soon after treatment of a migraine attack with sumatriptan injection; whether these were migraine-related or drug-related is discussed. None of the three myocardial infarctions was due to sumatriptan injection use. We conclude that sumatriptan injection is well tolerated when used in accordance with labeling.