Because of the concern that we were underestimating the prevalence of tuberculosis within the Latino community in San Francisco, we undertook a community-based screening program directed largely towards recent immigrants. Of 1,871 intermediate-strength (5 TU) tuberculin tests applied and read, 37 per cent of the reactions were greater than or equal to 10 mm. Significant reactions were found in 53 per cent of foreign-born persons compared to 7 per cent of those born in the United States. Persons older than 20 years of age were more likely to have significant reactions compared to younger Latinos. Among the foreign-born, the frequency of significant reactions was not influenced by the length of stay in the US or a history of BCG (bacille Calmette-Guérain) vaccination. Two foreign-born children were found to have current tuberculosis. The prevalence of tuberculin reactors among US-born Latino children was 3 per cent, which suggests that undetected transmission of tuberculosis may be occurring. We conclude that Latino immigrants should be systematically screened for tuberculosis.