The present study examined the ability of three headache groups (migraine, mixed migraine/tension, and tension) to accurately discriminate subjective levels of muscle tension at the forearm flexor, frontalis, and trapezius muscle sites. Discrimination ability was assessed at pre- and posttreatment using a psychophysical method of magnitude production. Results show that the ability to discriminate muscle tension levels at pretreatment varied across the headache groups, with migraineurs being the most accurate (r=.854), followed by the mixed headache group (r=.785), and finally the tension headache group (r=.732). Discrimination ability significantly increased at the posttreatment assessment. A multiple regression analysis showed that pretreatment performance on the muscle discrimination task significantly predicted outcome (r=.75) from relaxation and biofeedback training for migraine patients but not for the mixed or tension headache groups.