In this study, resting EMG levels were measured in the frontalis and temporalis muscle in patients suffering from muscle contraction headache, migraine, or mixed muscle contraction-migraine headache. The EMG levels of these groups were never significantly higher than those of a control group of subjects without headaches. Significantly higher levels, however, were found in both muscles in the migraine and mixed headache groups if the resting EMG levels were expressed as a percentage of the EMG level during maximal contraction. There was a tendency for proportional EMG levels of both muscles in the muscle contraction headache group to be significantly elevated. Headache patients generally showed lower maximal EMG levels than control subjects. The significance of this finding is discussed in relation to the etiology of the headaches. It is concluded that proportional EMG levels are a better index of the state of contraction than absolute EMG levels and are preferable in investigations of headache.