BACKGROUND: We investigated the effect of Retinoic acid in the growth of contralateral lung after pneumonectomy. METHODS: Twenty one adult male Wistar albino rats from the same colony were used. They were divided into three groups (Group A, B and C). Group A undergone only left posterolateral thoracotomy. In Group B and C, the rats were subjected to left posterolateral thoracotomy and left pneumonectomy. In Group C, rats were given intraperitoneal Retinoic acid during the operation and continued to be given everyday postoperatively. Rats were sacrificed on the 10th day and their total body, right lung weights and right lung volumes were measured. RESULTS: The volume and weight indices of the lung were found to be higher in Group C. In histopathological examination, there was a reduction in the mean number of alveoli in Group B and C. A significant rise in the mean dimension and average wall thickness of the alveolar structure were determined in Group C. CONCLUSION: Retinoic acid contributes to the compensatory growth of the residual lung tissue.