An investigation of the effect of electric fields at microwave frequencies on the induction of action potentials in excitable membrane systems is proposed. The objective of the research is to differentiate between effects due to the impressed microwave electric field as contrasted to other microwave-specific thermal and nonthermal effects. A waveguide irradiation technique will be used to expose the algae chara australis and other excitable cell systems to low intensity microwave radiation in the frequency range of from 2 to 4 GHz in a thermostated irradiation chamber. Initially continuous wave microwaves will be employed, followed by an investigation of pulse modulated fields. The cell systems will be of sufficient size to permit the measurement of action potentials with electrodes exterior to the waveguide, thus minimizing interactions between the microwave field and the detection system. Prior to microwave exposure the mean threshold electric field strength for the induction of the action potential will be determined by the use of a variable amplitude pulsed current stimulator. Thresholds will be redetermined during and after exposure of the cell system to microwave radiation of known field strength. Variations in the excitation threshold will be interpreted in terms of the summation of the field strengths of the impressed stimulus and the microwave field. The independent variables to be investigated will be microwave field strength, microwave frequency, pulse duration and amplitude, latency for recovery of pre-exposure threshold and temperature.