This invention relates to a process for inhibiting scale on metal surfaces exposed to an aqueous system, particularly a circulating aqueous system. The process comprises adding ethylenediamine-N,N-disuccinic acid, or salts thereof, to the aqueous system. Ethylenediamine-N,N-disuccinic acid, or salts thereof, act as a chelating agent and are biodegradable. The process is useful for inhibiting the formation of scale on metal surfaces of steam generating and cooling systems.