Low-level microwave energy at a frequency of 2.45 GHz has been previously observed to alter the firing frequency of Aplysia californica neurons. This study was undertaken to search out the mechanism of this microwave effect by examining the influences of microwave energy on specific ion currents across the cell membrane that influence the cell's firing frequency. Late outward K(+) current was examined and showed no statistically significant change during microwave exposure. The membrane current shape during voltage clamping (the summation of several different ionic currents) also showed no change during exposure except in one instance when exposure was concurrent with the application of Na(+) free artificial sea water. Keywords include: Microwave energy, Voltage clamping, Firing frequency, Neuronal activity, Aplysia californica neurons, Ionic currents, Microelectrodes, Ganglion, Stimulus Isolation Units.