The prevalence of tuberculin skin test reactions among intravenous drug abusers and differences in tuberculin skin test positivity between HIV-seropositive and HIV-seronegative subjects were evaluated in a cross-sectional study of 1131 subjects. They were recruited from a therapeutic community, from those who attended the centre for the treatment of drug addiction and from those who visited for any reason an acute tertiary-care hospital in Vitoria-Gasteiz, Basque Country (Spain). All subjects underwent skin testing with purified protein derivative (PPD) tuberculin and testing for HIV antibodies. CD4(+) T-lymphocyte count was determined in HIV-seropositive individuals. Positive PPD tests were recorded in 35% of drug users who were HIV-seropositive and in 65% in those who were HIV-seronegative. In the HIV-infected group, there was a significant association between results of the tuberculin test and CD4(+) T-lymphocyte count. When the CD4(+) T-lymphocyte count was > or = 500 cells/mm(3), percentages of positive PPD tests were similar in HIV-seropositives and HIV-seronegatives (47% versus 65%) but when the CD4(+) count was < 500 cells/mm(3), positive PPD tests occurred in only 21% of HIV-seropositives. The PPD test showed a decreased sensitivity for detecting tuberculosis infection in HIV-infected intravenous drug users with CD4(+) T-lymphocyte counts fewer than 500 cells/mm(3).