Impala Platinum Limited is the world's second largest platinum producer, producing more than 1.9 million ounces of the precious metal last year. As part of Impala's ongoing expansion programme, tonnage through their principal UG-2 processing facility, near Rustenburg, was increased by 25% in 2001. The expansion project achieved the increased throughput target but the anticipated recovery increase was not realised. Test work as part of an optimisation project indicated that open circuit regrind milling would significantly increase the overall recovery of the plant. Subsequently, the high grade regrind mill was converted from closed circuit to open circuit configuration, during September 2003, and a 3.7% recovery increase was realised. This paper attempts to explain the recovery increase achieved by examining and comparing metallurgical as well as mineralogical changes in mill product from before and after the open circuit conversion. Other initiatives implemented during the structured optimisation project have already been published by Martin 2 et al. [Martin, C.J., Nel, E., Raabe, H., 2004. PGM ore processing at Impala's UG-2 concentrator in Rustenburg, South Africa. In: Proceedings of 36th Annual Canadian Mineral Processors Conference, Ottawa] and will thus not be discussed any further. (C) 2005 Elsevier Ltd. All rights reserved.