In this study 11 myasthenia gravis patients (mean age of 37.72 years; range, 20-59; mean duration of illness, 4years; range, 1months-16years) where enrolled to study the SFEMG results of the masseter muscle. 10 normal individuals (mean age 34.3; range 22-55 years) where similarly studied to determine the normative values of SFEMG of the masseter muscle, and ultimately assess the sensitivity of this test in the diagnosis of myasthenia gravis.Examination of the masseter muscle yielded 100% sensitivity in this study, compared to 90% sensitivity for the EDC. The mean MCD of the masseter in the patient group was 63.4 us +/- 9.98 us, compared to 21.3 us+/- 4.9 us in the control group. The patient group showed 68.9 % +/- 27.4% abnormal pairs compared to 3.7% +/- 3.6% in the control group. The patient group also showed 37.5% blocking. Comparing the SFEMG results of the EDC with those of the masseter muscle, and the percentage of abnormal pairs of the two muscles showed a statistically significant difference (P= 0.02), while the percentage of blocking showed a high statistically significant difference (P= 0.000), indicating the masseter muscle to show a larger number of abnormal pairs and a higher percentage of blocking than the EDC muscle.