As part of the required screening process of illegal aliens applying for adjustment of status by the Immigration and Naturalization Service, 7,573 persons were evaluated for tuberculous infection by the Denver Department of Health and Hospitals from May 1987 through December 1988. Applicants were screened with tuberculin skin testing, chest radiographs, or both. Review of 6,520 charts that were available found that 4,840 applicants had tuberculin skin tests, of which 2,039 (42 percent) were > or = 10 mm and 1,528 had further evaluation at the Denver Metro Tuberculosis Clinic. Seventy-five percent of the applicants were between the ages of 15 and 34 years, and 91 percent were from Mexico. Evidence of past or current tuberculous infection on chest radiograph was present in 273 (17 percent) and 16 (7 percent) had sputum cultures obtained that identified four new cases of active tuberculosis. Isoniazid preventive therapy (IPT) was recommended to 1,029 applicants, of whom 29 (3 percent) were 35 years of age or older; 716 (70 percent) completed at least six months of treatment. We conclude that there is a high prevalence of tuberculous infection in foreign-born persons applying for adjustment of immigration status, but a low prevalence of clinically apparent tuberculosis. This population is an excellent target for IPT, which can be achieved with good success. Proactive screening and preventive therapy is likely to significantly reduce tuberculosis reactivation and morbidity, prevent secondary infection of contacts, and be cost-effective.