Of 132 infants with severe lower respiratory tract disease, 70% had a history of daily heavy smoke exposure from cooking and/or heating fires. Only 33% of 18 infants free of respiratory problems had such exposure. Wood smoke is a potent risk factor in the development of severe lower respiratory tract disease in infants. Lower social class, and sibling and parental symptoms (often cited as risk factors), may also be expressions of the same smoke-filled room. Parents of newborn infants should be told to keep smoke away from their baby, especially if ethnic traditions predicate exposure.