The electroneurographic study in 29 patients, during treatment with isoniazid for pulmonary tuberculosis in a 12 months period is reported. The patients age were between 16 and 70 years. During the study period motor nerve conduction velocity was done every two months in the median, ulnar and peroneal nerves. The statistical analysis in a 6 months period, revealed p > 0.05 (non-significant) at the median and peroneal nerves, in spite of the lowering of the motor nerve conduction in a 12 months period. The same findings were observed with the ulnar nerve, but p < 0.01 (significant). It was impossible to establish a correlation between the motor nerve conduction velocities and the clinical findings observed in the patients. This paper, in the author's opinion, shows that the nerve motor conduction technique is worthless in the follow up of isoniazid treated patients.