The addition of cement to underground backfill at The Zinc Corporation, Limited and New Broken Hill Consolidated Limited, Broken Hill commenced in 1967. This resulted in a deterioration in metallurgical performance with increased loss of lead and zinc to residues at each concentrator. Investigations to determine the cause of the problem and methods to counteract it have been undertaken. This paper outlines the effects of cement on lead-zinc beneficiation at Broken Hill and presents an interim report on attempts to overcome the metallurgical Deterioration.