There is evidence to suggest that the human immunodeficiency virus (HIV) can be transmitted from mothers to their uninfected offspring via infected breast milk. The quantitative risk of transmission by this route is unknown. We must urge all individuals at risk for HIV infection to be tested. In the United States, it is recommended that women who are known to be HIV-positive be discouraged from breast-feeding. In certain regions of the United States, such as high-risk areas of New York City, HIV infection may be present in more than 3% of reproductive-age women, most of whom do not know they are infected. Women who either live in areas of the United States in which acquired immunodeficiency syndrome (AIDS) is endemic or are living in other parts of the country and are at high risk for AIDS, yet refuse to be tested, should be counseled regarding the potential for transmission of the virus to uninfected offspring via breast-feeding.