Most of the commonly used antituberculosis drugs are excreted in the breast milk of nursing mothers. However, only a small fraction of the adult dose appears in breast milk, and we estimate that breast-fed infants would receive no more than 20% of the usual therapeutic dose for infants for any of these drugs. Based on these considerations, we believe the risk of toxic reactions to drugs in infants of nursing mothers receiving antituberculosis drugs is very low. Nevertheless, the decision to breast-feed while taking antituberculosis drugs must be an individual one that takes into account the known facts, professional opinion, and the patient's values and preferences.