A silver rotating disc electrode has been used to measure the ionic cyanide (CN(aq)-) concentration in gold leaching circuits amperometrically. When the electrode is held at 0.1 V vs SHE the current flow is proportional to the cyanide concentration. In laboratory solutions the correlation coefficient ranged from 0.9999 at 30 degrees C to 0.9995 at 50 degrees C. The method is free from interference from the anions expected at gold plants, except sulphide, which, if present, can be removed by precipitation with lead(II). Cyanide bound up in stable metal complexes decreases the available CN-, and is not measured by the method. Other than by complexation, the metals ions studied did not interfere with the method. CN(aq)- converted to HCN(aq) at low pHs is also not measured except on addition of a pH buffer. The results are consistent with those from a silver nitrate titration, that also does not measure HCN(aq) or strongly complexed cyanide. Laboratory and field trials have shown that the method will work in leaching slurries without filtration, but regular electrode cleaning is required to ensure accurate results.