A new test that measures interferon-gamma (IFN-gamma) release in whole blood following stimulation with tuberculin has the potential to detect tuberculosis infection using a single blood draw. The IFN-gamma release assay was compared with the standard tuberculin skin test (TST) among 467 intravenous drug users at risk for tuberculosis in urban Baltimore. Among 300 human immunodeficiency virus (HIV)-seronegative patients, the IFN-gamma release assay was positive in 177 (59%), whereas the TST was positive in 71 (24%), for a percent agreement of 59% (kappa=26%). Among 167 HIV-seropositive subjects, the IFN-gamma release assay identified 32 reactors (19%); the TST identified 16 reactors (9.6%), for a percent agreement of 82% (kappa=28%). The IFN-gamma release assay detected more reactors than did the TST, but its agreement with TST was weak. As the TST is an imperfect standard, further evaluation of the IFN-gamma release assay among uninfected persons and persons with culture-confirmed tuberculosis will be useful.