Patients undergoing organ transplantation require potent and often prolonged immunosuppressive therapy. These patients therefore, have an increased risk of a variety of infections, including mycobacteria. Furthermore, because the host responses to these infections are modified, these patients may often present with a typical features, making the diagnosis difficult and the response to therapy suboptional. Several factors contribute to the high incidence of infection in solid organ transplant recipients. These patients are often immunocompromised because of their underlying condition (e.g. uremia, liver failure, malnutrition). In addition, therapeutic IS to prevent graft rejection is probably the most important factor contributing to infection in transplant recipients.