SummaryThe activity patterns of the masseter and the anterior temporal muscles were studied in twenty‐one healthy male subjects while clenching at 10, 20, 30, 40 and 50% of the maximum clenching level. At low clenching levels the temporal muscle activity tended to dominate, at high levels the masseter muscle activity was stronger (P<0.001). The asymmetry in muscle activity also depended upon the clenching level (P<0.001), while at each level the masseter muscle asymmetry was greater than the temporal muscle asymmetry (P<0.05–P<0.025). By comparing the electromyographic activities of the left and right side within each subject it was found that the masseter muscle with the higher electromyographic activity tended to have the larger cross‐sectional area (P<0.01) and at the 50% clenching level it tended to be on the side with the greater number of post‐canine tooth contacts (P