The viability of the human fetus increases significantly beyond 25 weeks' gestation as the lung development progresses towards the 'saccular' stage. We report on a fetus of 22 weeks' gestation whose lung maturation was accelerated by 4 weeks, most likely due to the unintentional exposure to the retinoid isotretinoin (13-cis-retinoic acid) during pregnancy. Although retinoids are known to be stored within the lungs and to play a key role in lung differentiation and growth, their storage within the lung is limited during this critical developmental period. Even though glucocorticosteroids are used clinically to enhance lung maturation in the face of impending preterm birth, there are no data yet which demonstrate that glucocorticosteroids, when given alone, are effective in promoting lung maturation prior to 24 weeks' gestation. Strong evidence however, indicates that glucocorticosteroids promote the utilization of lung retinoids immediately before birth. Our observation of increased lung maturation, in conjunction with the above information suggests that retinoids alone or in combination with glucocorticosteroids might promote lung maturation more effectively than glucocorticosteroids alone when birth seems inevitable at a very early gestational age.