The mechanism of adsorption of aurocyanide onto activated carbon and its subsequent elution are examined in this study, with special reference to the effects of acid and alkali treatment on the system. The results, including a careful analysis of the distribution of all ions in the adsorption and elution processes, are discussed, and evidence for the adsorption and elution mechanisms involved is presented. It is proposed that, under normal plant conditions, aurocyanide is extracted onto activated carbon in the form of an ion pair, M(n+)[Au(CN)2(-)]n, and eluted by hydroxide or cyanide. The hydroxide or cyanide ions react with the carbon surface, rendering it relatively hydrophilic with a decreased affinity for neutral species. Additional adsorption mechanisms are shown to operate under other conditions of ionic strength, pH, and temperature, and it is suggested that this may account in part for the lack of agreement among workers.