The study was designed to compare the response to almotriptan in migraine patients who take medication early in the course of the attack with that when medication is taken after pain has become moderate or severe. A randomized, four-arm, multicentre, multinational, double-blind, placebo-controlled trial of almotriptan (12.5 mg) comparing treatment administration when pain intensity was mild and within 1 h of headache onset vs. pain that had become moderate or severe was conducted. Of 491 migraineurs enrolled, 403 were evaluable [intention-to-treat population (ITT)]. Their mean age was 38 years, 84% were female and they had a mean of 3.7 attacks/month. Of these patients, 10% did not take medication according to their randomly allocated basal pain intensity (mild or moderate/severe) and were subsequently reassigned to that group for this analysis-'Act when Mild (AwM)' group. In the almotriptan arms, 53% of mild basal pain and 38% of moderate/severe basal pain patients were pain free at 2 h (P = 0.03; primary end-point). Corresponding proportions in the placebo groups were 25% and 17% (statistically significant vs. respective almotriptan arms). Secondary end-points (ITT) were also significantly in favour of early intervention with almotriptan, both between and across treatment groups, such as sustained pain free: 45.6% vs. 30.5% (P = 0.02). Adverse events were reported in < 5% of treated patients in all groups (NS), with no serious events. Treatment with almotriptan while migraine pain is still mild provides statistically significant and clinically relevant enhancements in efficacy compared with treatment when pain has reached higher severity levels.