New drug classes, biologics, have been developed over the past 10 years based on human or chimeric antibodies against cytokines or receptors with pivotal roles in the inflammatory pathways of immune-mediated inflammatory disease. Anti-tumor necrosis factor agents carry the largest infection risk of all the biologics, predisposing patients to mycobacterial infections. Patients receiving biologics are at higher risk for developing tuberculosis. New cases of tuberculosis or reactivation of latent tuberculosis infections may occur during the course of treatment, so a high level of vigilance is highly recommended. © 2009 Elsevier Inc. All rights reserved.