Corrosion problems have been encountered in reactors used in pilot plants for the development of different bacterial leaching (bioleaching) processes, A large part of this corrosion is attributable to bacterial activity, i.e. biocorrosion, and basic information is needed for a better understanding and control of this phenomenon, The bioleaching solution associated with the presence of bacteria is highly acidic and requires the use of highly corrosive-resistant steel. The selection of materials for the manufacture of industrial bioleaching reactors is difficult and random. Consequently, it is now essential to study the behavior of selected stainless steels during bioleaching in order to determine their potential suitability for industrial use. The main objective of the present study is to compare the respective resistance of two such steels to various types of corrosion and determine which of the steels is most appropriate for manufacturing reactors at an industrial scale. The corrosive medium was a solution generated during the bioleaching of a cobaltiferous pyrite, where a bacterial population comprised of three species was used. Metal coupons and electrodes were made out of two grades of stainless steel and their corrosion during bioleaching was monitored by methods based on the weight loss of the coupons and on the electrochemical behavior of the stainless steel electrodes. By combining the weight loss and electrochemical results, it has been possible to show that (i) the two steels have a similar and satisfactory behavior, with a corrosion-erosion rate of less than 25 mum/year, and (ii) samples left for more than 1 month in the medium are not affected by localized corrosion, thus confirming the accelerated corrosion tests indicating the high resistance of the two stainless steels to localized corrosion.