Nerve conduction study is invaluable in clinical neurology, especially for assessing penpheral neuropathies. Abnormal nerve conduction studies may result not only from peripheral nerve dysfunction itself, but also from other various mechanical, technical, and physiological factors. Recently developed electromechanics and standardization of the techniques minimize the variability of nerve conduction studies but physiological factors such as age, sex, and height are not correctable. There are numerous controversies ooncemulg the posslble effects of various physiological factors on the results of nerve conduction studies, probably, in my personal opinion, due to rather small size of the population obtained in the previous studies. Furthermore, the physiological factors them selves are not independent variables to have effect on nerve conduction studies, but they seem to be interrelated. In this study, the results of nerve conduction study on 639 Korean adults over the age of 20 without any suspicion of neurological deficits were analysed to determine the effect of a single independent physiological factor as well as the combined effects of several physiological factors. The results are as follows:1. The nerve conduction velocities varied according to the segments of the tested nerves. The velocities of the upper extremity and proximal segments were faster than those of the lower extremity and distal segments. 2. Comparing my result with those from other laboratories, the interlaboratory variability of nerve conduction velocity seems to be technical. 3. Physiological factors such as sex, age, and height seem to affect the results of nerve conduction studies independently. But stepwise multiple regression analysis has to be utilized because there are statistically significant interrelations between sex and height and between age and height 4. On the stepwise multiple regression anaiysis of the nerve conduction velocities, the sex differences are recognized over the elbow segment of the ulnar motor nerve, the dis.