Biological leaching of nickel laterite ores is based on the use of heterotrophic microorganisms and their metabolic products to dissolve nickel and cobalt from oxide minerals. High salinity of water supplies and soils in the vicinity of nickel laterite ore bodies can be a major challenge in the application of bio-leaching process in situ. Salt stress can imbalance the osmotic potential in fungi cells generating a water deficit and the influx of sodium may lead to metabolic toxicity. The purpose of this study is to examine salt tolerance development of Aspergillus foetidus using gradual acclimatization technique to salt concentrations up to 2% and to assess the use halotolerant microorganisms in leaching weathered saprolite ores under saline conditions. It has been observed that salinity stress affects the growth but not the energy metabolism of the organism. Kinetic of metal leaching, nature of secondary reactions and metal dissolutions were also influenced by salt stress. (C) 2006 Elsevier Ltd. All rights reserved.