SYNOPSISFree and total plasma tryptophan (TRY) was evaluated in migraine and daily headache sufferers. In migraineurs, free plasma TRY was significantly higher on the day of the attack, the day preceding and subsequent to the attack in comparison with controls.The possibility that in migraineurs a lowering of brain 5‐HT may displace TRY from its binding to plasma albumin through an unknown feedback mechanism is suggested. In daily headache sufferers total plasma TRY levels were statistically significantly lower compared with controls. This may reflect a deficiency of 5‐HT in the br