Splenius capitis (SPL) electromyograms were recorded using conventional surface and intramuscular wire electrodes simultaneously during various head-neck movements and isometric tasks to test the selectivity of surface electrodes for SPL myoelectric signals. The insertion of bipolar wire electrodes was aided by a computerized tomographical study of each subject's neck. Surface electrodes were placed over the superficial SPL area. Head motion was recorded with an electromechanical device. The selective SPL wire recordings confirmed that SPL has two main functions: ipsilateral rotation and extension. It also plays a subordinate role in ipsilateral tilting of the head. Intramuscular and surface recording results were contradictory mainly for flexion and contralateral rotation. These discrepancies appeared to be due to 'cross-talk' from adjacent muscles, particularly from the sternocleidomastoid muscle. We conclude the validity of electrode recordings is questionable for SPL and most dorsal neck muscles, especially during isometric tests.