Screening for tuberculosis (using the Mantoux test) and human immunodeficiency virus (HIV) was conducted among intravenous drug users (IVDUs) recruited from a San Francisco Bay Area neighborhood. Of 178 IVDUs skin-tested with one commercial purified protein derivative (PPD) preparation, a reaction of ⩾5 mm ofinduration occurred in 62 (470/0) of 133 HIV-negative and 13 (29%) of 45 HIV-positive IVDUs (P =.037). Forty-two IVDUs with an initial PPD reaction ⩾5 mm were retested with a second commercial preparation; 11 (26%) had no reaction (0 mm) on retesting. These 11 were 5 (56%) of9 HIV-positive and 6 (18%) of33 HIV-negative persons (P =.038). These discrepancies may be unique to specific lots of product or may reflect more general differences. A degree of caution in evaluating unexpected tuberculin skin test results may be indicated. Response to different tuberculin products by HIV status should be further evaluated.