Different electrophysiological tests were performed on 25 myasthenic patients and 34 randomly selected healthy subjects which were regarded as the control group. Myasthenic patients were studied in four subgroups according to the different modalities of treatment. Four patients were studied before the start of any treatment; four were studied while on Pyridostigmine (Anticholinesterase drug); another four were studied being on steroids, and thirteen patients were studied aftter being thymectomized. Nerve conduction studies for the both the median and ulnar nerves revaled no significant difference between the patients and the control groups. EMG during volitional effort showed a maximal decrease in the MUAP during in the proximal muscles, the Deltoid, in the non treated group which was insignificant compared to the control group. The polyphasic percentage was significantly increased proximally in the deltoid muscle compared to the control group. All the three modalities of treatment; Pyridostigmine, steroids and thymectomy increased the mean durations of the Deltoid muscle. Pyridostigmine decreased the polyphasic percentage significantly, while thymectomy decreased it insignificantly, both compared to the control group. On the contrary, steroids induced steroid myopathic pattern of increased polyphasic potentials of short durations and low amplitudes. All the control subjects did not show an abnormal decrement neither proximally nor distally. In the patients group, the majority showed an abnormal decrement proximally and it was evident that there was a significant difference between the proximal and distal muscles. Pyridostigmine made the best improvement in the decrement test, thymectomy steroids are next successively In the determent test postactivation exhaustion was demonstrable in the thymectomy patients and could be of help as an aid in tlie diagnosis of MG. patient of grade HB having a malignant thymoma with a thymectomy performed only in the course of the disease (< 1 year duration) showed a better importement in their decrement test abnormalities than those of grade IIA having a begin hyperplasia of the thymus with a thymectomy performed late in the course of the disease (.2 years duration). Post-tetanic potentition was observed in all the non treated myasthenic pyridostigmine was the best to correct this abnormality, next is steroids and thymectomy in successive manner T/A ratio showed a significant increment in the non treated myasthenic to group compared to the control group. The Pyridostigmine and steroid treated patient were Improved but insignificantly, while thymectomized patients showed the least improvement1 year duration) showed a better importement in their decrement test abnormalities than those of grade IIA having a begin hyperplasia of the thymus with a thymectomy performed late in the course of the disease (.2 years duration). Post-tetanic potentition was observed in all the non treated myasthenic pyridostigmine was the best to correct this abnormality, next is steroids and thymectomy in successive manner T/A ratio showed a significant increment in the non treated myasthenic to group compared to the control group. The Pyridostigmine and steroid treated patient were Improved but insignificantly, while thymectomized patients showed the least improvement.<1 year duration) showed a better importement in their decrement test abnormalities than those of grade IIA having a begin hyperplasia of the thymus with a thymectomy performed late in the course of the disease (.2 years duration). Post-tetanic potentition was observed in all the non treated myasthenic pyridostigmine was the best to correct this abnormality, next is steroids and thymectomy in successive manner T/A ratio showed a significant increment in the non treated myasthenic to group compared to the control group. The Pyridostigmine and steroid treated patient were Improved but insignificantly, while thymectomized patients showed the least improvement.