Repetitive nerve stimulation test(RNS) was performed on 32 patients with myasthenia gravis who showed positive response to the tensilon test. The result of the repetitive stimulation test before and after the tensilon injection was compared with the point of improvement of the CMAP and decremental response. The results were as follows: 1. All patients with myasthenis gravis showed decremental responses to the low rate of stimulation in RNS. 2. The results after tensilon injections showed significant improvements of the CMAP in ocularis oculi(OOC), flexor carpi ulnaris(FCU)(P <0.0005), deltoid and abductor digiti quinti muscles(ADQ)(P < 0.005). 3. There were improvements of decremental responses after tensilon injection. 1) At 2/sec, there were significant improvements in the muscles of ADQ(P <0.005), deltoidl OOC and FCU(P < 0.0005). 2) At 3/sec, there were significant improvements in the muscles of OOC(P <0.005), deltoid, FCU and ADQ(P < 0.0005). 3) At 5/sec, there were also significant improvements in all the muscles of OOC, deltoid, ADQ, FCU(P <0.0005). These results showed that tensilon improves the RNS abnorrnalities in myasthenic patients with positive tensilon test. We think these findings before and after the tensilon injection are helpful to diagnose and differentiate a patient with suspected myasthenia gravis who has a negative tensilon test or insignificant RNS findings.