Pulmonary emphysema is a common disease¹ in which destruction of the lung's gas-exchange structures (alveoli)² leads to inadequate oxygenation³, disability⁴ and frequently death¹; lung transplantation provides its only remediation. Because treatment of normal rats with all-trans-retinoic acid increases the number of alveoli⁵, we tested whether a similar effect would occur in rats with emphysema. Elastase was instilled into rat lungs, producing changes characteristic of human² and experimental⁶ emphysema: increased lung volume reflecting a loss of lung elastic recoil, larger but fewer alveoli and diminished volume-corrected alveolar surface area due to destruction of alveolar walls. Treatment with all-trans-retinoic acid reversed these changes providing nonsurgical remediation of emphysema and suggesting the possibility of a similar effect in humans.