The design of a new instrument for routine analysis of electroactive substances is presented. The instrument is a potentiostat in which potential control is maintained by varying the rate of delivery of current pulses of uniform charge content to a small electrochemical cell. Digital readout of the concentration in desired units is obtained by counting and displaying the number of current impulses. The entire analysis consists of introducing a sample, pressing the potentiostat button and reading the result within 3–5 seconds - hence the name, “push-button analyser”. A block diagram, schematic diagrams and parts list are included.