Newborn infants are thought to be particularly susceptible to infection with Mycobacterium tuberculosis, and the possibility of exposure to unrecognized clinical tuberculosis in nursery and hospital personnel is ever present. To reduce this possibility, periodic skin testing of hospital personnel is often carried out, and tuberculin-positive personnel are given preventive treatment with isoniazid (INH). Also, environmental controls, such as ultraviolet light and periodic air exchange, are used. The efficacy of these measures has not been fully established. A nursery supervisor with smear- and culture-positive pulmonary tuberculosis and a productive cough exposed 528 newborns over a three-month period before her disease was diagnosed. All 514 infants available for skin testing at approximately 3 months of age had negative skin tests. None received isoniazid preventive treatment. The nursery rooms all had ultraviolet lighting mounted above eye level. Calculated air changes per hour with positive pressure ventilation of fresh air ranged from 12 to 18. The hospital did not regularly test employees for tuberculosis. Periodic tuberculin testing of hospital personnel with preventive treatment of reactors presumably would have prevented this exposure.