1. An experimental method of recording and controlling the membrane potential of a small area of the membrane of the cockroach giant axon is described.

2. The recorded action potentials were essentially similar to those previously recorded by other methods.

3. The membrane currents resemble those reported for the squid axon, the node of Ranvier in frog nerve and the lobster giant axon.

4. Small cathodal polarizations gave only small outward currents; larger depolarizations (10-100 mV.) gave an initial inward current which changed into a delayed outward current.

5. The initial inward current attained a maximum with depolarizing pulses of 40-50 mV. and showed a reversed, outward, flow of about 100 mV.

6. Delayed outward currents increased continuously with increasing impulse voltage.

7. The initial inward current was larger when the pulse was preceded by an hyperpolarizing prepulse.

8. It is concluded that, although the early inward currents were in all probability related to Na+ ions and the delayed outward currents to K+ ions, the possible participation of Ca2+ and Cl- ions to the ionic currents cannot be excluded.

Most experiments have been carried out in the 1st Department of Physiology, University of the Saarland, Homburg, Germany