The protean effects of undernutrition on lung defenses and repair capabilities suggest that less than adequate nutritional support is a key pathogenetic factor in the development of bronchopulmonary dysplasia (BPD). Very-low-birthweight (VLBW, less than or equal to 1,000 g) premature infants who require intensive respiratory support have a distressingly high incidence of chronic lung disease or BPD. Many VLBW infants are currently undernourished during the most acute phase of their respiratory illness. Because VLBW newborns have only meager caloric reserves (fat, glycogen), and have only marginally sufficient stores of nutrients needed for effective lung defenses and repair capacity (vitamins A and E, copper, zinc, iron, selenium, essential fatty acids, etc.), the adequacy of nutritional support provided them will almost certainly influence their ability to tolerate early stress, and it may play a critical role in their clinical outcome. Experimental studies, combined with a limited number of clinical studies, clearly demonstrate that undernutrition can interact with each of the other well-accepted etiologic factors involved in the pathogenesis of BPD. Nutritional status affects the lung's ability to resist hyperoxic damage, to replace damaged/sloughed lung cells caused by barotrauma, to promote continued lung growth, to resist infection, and to tolerate prolonged and potentially toxic stresses in general. By providing more ideal nutritional support, clinicians may be able to apply preventive treatment to influence the outcome of intensive respiratory therapy in the VLBW newborn.