SUMMARY A new potentiostat-cell system design for application to the study of very rapid electrochemical processes is described. The potentiostat provides submicrosecond transient response with very high current capability. The cell is constructed such that electrode placement can be determined very accurately and reproducibly. Very-small-diameter Luggin capillary probes have been employed to allow minimum separation between the working electrode and the reference probe, with subsequent minimization of uncompensated resistance. Probe dimensions could be varied conveniently and accurately to obtain specific characteristics. The response characteristics of the potentiostat-cell system were defined and optimized. The potential gradients near the working electrode for high-frequency control signals were measured. Controlled-potential electroanalytical methods were applied to the study of several electrode processes whose behavior could be predicted for rapid experiments.