The voltammetric behavior of samples contained in the pores of a platinum working electrode with pore diameters on the order of 0.5 mu m was investigated. Electroactive species dissolved in supporting electrolyte are contained only within the working electrode. while the reference and counterelectrodes are located in the external supporting electrolyte solution. Species confined to the pores are coulometrically electrolyzed during potential step or scan experiments because of the very short diffusion distances to the electrode surface. The experimental results were compared with the theoretical thin layer linear sweep voltammetric equation derived by Hubbard and Anson(1) and good agreement was obtained. Background current correction was performed automatically using the computer to subtract a stored background. Subtraction was performed either in the digital mode simultaneously with acquisition of the data or in the analog domain by converting the digitized background signal to an analog current which was injected synchronously into the summing point of the current-to-voltage converter during the scan. Data obtained in potential step experiments were used to obtain an internal volume of the platinum working electrode of 19.0 mu l.