The aim of the research was to obtain basic data on the aerobic metabolism of potassium cyanide. Studies were conducted on activated sludge cultures fed cyanide as their only source of carbon and nitrogen at hour and one-half hour intervals and continuously. It was shown that these cultures could metabolize the cyanide converting the carbon to carbon dioxide and the nitrogen to ammonia, nitrite, or nitrate. Little growth was realized in these systems although suspended solids could be maintained. Further studies showed that a cyanide acclimated culture readily metabolized a cyanide-acetate feed with the acetate producing considerable growth in the system.