The reproducibility of electromyographic parameters descriptive of deliberate unilateral chewing (activity, timing, curve symmetry) was investigated in normal asymptomatic volunteers. The best time for the initiation of muscle activity was also examined, with the future aim of staging TMJ internal derangements. The results suggest that activity is the most reliable variable, indicating that it may be helpful in describing muscle incoordination. When time was used in conjunction with another variable, overall reproducibility decreased.