Since the initial electroanalytical application of glassy carbon electrodes ~, many reports have appeared dealing with analytical uses 2-9, determination of stability constants ~Β° and mechanistic studies ~L12. The difficulties inherent in work with solid electrodes are well known, but each of the above reports suggested its own surface pre-treatment procedure which led to satisfactory reproducibility. We now present rate data for some electron transfer reactions at glassy carbon electrodes, together with observations on the effect of time and of surface treatment on electron transfer kinetics. EXPERIMENTAL Glassy carbon electrodes, type GC-A were obtained from the Tokai Electrode Mfg. Co., Japan in the form of 6 mm diameter cylinders and were mounted in glass tubing using epoxy resin*. Electrical contact was achieved by cementing copper wire to the inner carbon surface using silver-loaded Araldite. Some measurements were made on shielded electrodes but in most cases unshielded electrodes were employed so that the effects of surface polishing could be ascertained. Comparison measurements were performed on hanging mercury drop electrodes (Metrohm BM. 5-03), carbon paste 13 (CPE), wax-impregnated graphite 14 (WIG), and platinum electrodes (Titron 351 B, similar to the Beckmann 39273). A Servomex motor speed controller type MC43 controlled the motor-generator employed for rotating disc studies. All measurements were performed at 25,0Β°C in a thermostatted glass cell, having a Perspex lid drilled to hold the electrodes and inlet and exit tubes for high purity nitrogen used for deoxygenating the solutions. The potentiostat was based on the design of Harrer et al. ~5 and the reference electrode was Ag/AgC1 in saturated KCI. For cyclic voltammetry the potentiostat was programmed by a Hewlett-Packard 3300A function generator with a 3302A trigger/phase-lock plug in, and current-potential curves were recorded on a Riken Denshi D-5N X-Y recorder. Galvanostatic transients were observed, after prior potentiostatic polarisation, using the method of Bockris et al. 16 and photographed on Polaroid film * Later measurements on electrodes mounted in heat-shrinkable Teflon tubing gave identical rate constants.