This study presented a systematic observation on the human peripheral nerves by Karnovsky histochemical method for acetylcholinesterase (AChE). Some major nerve trunks and their branches from twenty upper limbs, a part of the muscular and cutaneous nerves of the lower limbs, and the ventral and dorsal roots and the gray communicating rami of C_7 from six human cadavers were obtained within 3 hours postmorten for this study. In the sensory nerve fascicles, the myelinated axons failed to react and the unmyelinated fibres showed strong enzymatic activity. In the motor nerve fascicles, 58% of the myelinated axons showed enzymatic activity, while the unmyelinated fibres which showed strong enzymatic activity, were much less than those in the sensory nerve fascicles. 87% of the myelinated axons in the ventral roots from the C_7 showed morphologically the same enzymatic activity as those in the motor nerve fascicles. The myelinated axons failed to show an enzymatic activity and the unmyelinated fibres showed very slight enzymatic activity in the dorsal roots. A strong enzymatic activity was shown in the gray communicating rami. Thus it is clear that both myelinated and unmyelinated fibres show different enzymatic activities in the motor and sensory nerve fascicles, and that those myelinated fibres showing enzymatic activity originate from the ventral roots and the unmyelinated fibres showing strong enzymatic activity originate from the gray communicating rami.