Different process options for the bioleaching of nickel-copper containing sulphide concentrates were evaluated. Tests in continuously operated reactor systems showed >98% nickel extractions over a range of temperatures, whereas for copper occurring as chalcopyrite, extractions of >95% could only be achieved at 70 C. During further optimisation of the process the effects of process parameters such as grind size, residence time, redox potential and feed solids concentration on the leach kinetics, metal extractions and performance of both moderate thermophile and thermophile cultures were addressed. Redox control in the first-stage reactor of thermophilic systems resulted in considerably faster copper leach rates and extractions of up to 95% could be achieved at increased feed concentrations and coarser grind sizes. High redox levels in the secondary reactors ensured >98% nickel recoveries. These operating conditions and control strategies have the potential to increase the rates of nickel and copper extractions to the extent that leaching times could be considerably reduced. (C) 2011 Elsevier Ltd. All rights reserved.