This study presents a flow injection system for the sequential determination of free (CN(-)) and total (CN(-)+ HCN) cyanide using a potentiometric method which employs two different processes for the determination of these two chemical species. The first process is based on direct detection of CN(-) using an ion-selective electrode for cyanide. In the second process, the sample is mixed with acid, and the released HCN is transferred across a PTFE membrane. The flow system employs three solenoid valves, a gas diffusion chamber, an ion-selective electrode, a potentiometer, and a computer with an AID conversion card. A Turbo Pascal computer program automatically performs all the steps involved in data acquisition and processing. The standard deviation for the results obtained with the proposed method was 0.5%.