Due to the highly refractory nature of Olympias pyrite concentrates, an oxidative pretreatment step is required to render gold amenable to the subsequent cyanide leaching. To exploit this resource research has been carried out into the potential use of the bacterial oxidation process either as an alternative or in conjunction with the commercially used aqueous pressure oxidation process. State of the art analytical techniques were used to identify the mode of gold occurrence within the concentrate and several parameters critical to the operation of biooxidation processes were evaluated. Results indicate that biooxidation techniques may be applied to many pyritic ores and concentrates since the mechanisms of bacterial attack on arsenopyritic and pyritic materials have been clearly identified. With this information it is possible to design a biooxidation system to meet the requirements of a particular feed material. However, testing of a proposed feed material will be required to comfirm the design parameters.