The purpose of this study was to determine the relationship between tongue position and mandibular muscle activity. Thirty-three subjects (28 women) between the ages of 18 and 34 years (mean = 22.1 years) with no prior inju ry to or pain in the jaw, mouth, or tongue participated in the study. Subjects were asked to rest quietyly while baseline electroymyographic recordings were made from the temporalis, masseter, and suprahyoid muscle regions. Afterwards, subjects were randomly assigned to conditions requiring them to position the tongue either against the anterior palate or on the floor of the mouth, making sure the tip does not press against any part of the mouth. The results indicated that right temporalis activity was higher when the tongue was positioned against the roof of the mouth than when it was either at baseline or resting on the floor of the mouth (P .03). A similar pattern of results was observed for the suprahyoid muscle group (P .01). There were no significant differences in masseter muscle activity as a function of tongue position (Ps > .20). These findings suggest caution in labeling the rest position of the tongue and indicate that further study of the relationship between tongue position and orofacial pains is needed.