We investigated the threshold of the platelet release reaction during the luteal phase of the cycle in 46 patients suffering from menstrual migraine (MM) and 27 healthy normal women. The distribution in both groups of the three types of aggregometric curves (types 1, 2 or 3) obtained in response to ADP 1 microM as aggregating agent was evaluated. Among MM sufferers, 19 (41%) showed a type 1 curve, while 14 (31%) had a type 2 curve and 13 (28%) showed an irreversible aggregation with a type 3 pattern. Curve distribution in controls was 18 (67%) for type 1, 8 (30%) for type 2 and 1 (3%) for type 3. A significantly (p < 0.05) different distribution of the three curve types between MM and controls was present, suggesting that a secondary wave of aggregation is more frequent in MM; the highest difference was due to the observed frequencies of type 3 curves.