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Objective: The development of neonatology and the availability of pulmonary surfactant have been helpful in effective reduction of the mortality of very low birth weight infants at the expense of an increasing number of survivors with bronchopulmonary dysplasia (BPD) caused by lung immaturity. BPD is a common syndrome in newborns, especially in preterm infants, when treated with hyperoxia and mechanical ventilation. Unfortunately, there have been no effective measure for the prevention and treatment of BPD. The purpose of this study was to investigate the influence of recombinant human insulin-like growth factor-1 (rh-IGF-1) on cell apoptosis and Clara cell secretory protein (CCSP) expression during the lung injury induced by hyperoxia, so as to assess its effect on the inflammatory lung injury and its developmental repair., Methods: Eighty full term neonatal Wistar rats under the same condition were divided randomly into four groups on the second day after birth. Group I was air control, group II was exposed to hyperoxia, group III air + rh-IGF-1, and group IV was treated with hyperoxia + rh-IGF-1. The pups in the control group were kept in room air, while pups in hyperoxia group were kept in a Plexiglas chamber and exposed to over 85% oxygen. Pups in group III were under the same raising condition except for exposure to room air and treated with intraperitoneal injection of rh-IGF-1 (1 microg/Kg) everyday from the third day. Pups in group IV were treated with intraperitoneal injection of rh-IGF-1 (1 microg/Kg) everyday from the third day of exposure to hyperoxia. Lung tissue sections of the neonatal rats were stained with hematoxylin and eosin (HE) after 7 d of hyperoxia exposure, expression of CCSP was examined by immunohistochemical method, and apoptotic cell index of lung tissue was calculated by using TUNEL method., Results: It was observed from immunohistochemical examination that positive staining of CCSP was distributed mainly in distal and respiratory bronchioles. The percentage of Clara cells in distal and respiratory bronchioles epithelium decreased in hyperoxia group (32.17 +/- 3.19)% compared to that in air control group (68.32 +/- 2.04)%, P < 0.01. Statistically significant differences were found in intensity of positiveness of Clara cells between hyperoxia (29.45 +/- 5.56) and air control group (42.37 +/- 3.24), P < 0.01. TUNEL assay showed that most apoptotic cells were alveolar and bronchial epithelial cells. The apoptotic index increased significantly in the hyperoxia group (55.77 +/- 6.09)% compared to the air control group (16.41 +/- 4.01)%, (P < 0.01). The positive rate (52.98 +/- 2.68)% of Clara cells and the expression (41.22 +/- 6.36) of CCSP in hyperoxia + rh-IGF-1 group increased significantly when compared with hyperoxia group, and the differences between these two group were also statistically significant (P < 0.01). The apoptotic index increased significantly in the hyperoxia + rh-IGF-1 group (27.98 +/- 3.09)% compared to the hyperoxia group (P < 0.01)., Conclusions: Hyperoxia exposure can promote the pneumocyte apoptosis and inhibit the expression of CCSP. Rh-IGF-1 can remove the block of the formation of lung alveoli, increase the secretion of CCSP, mitigate inflammatory responses in airway and alleviate lung injury via pneumocyte apoptosis. Therefore, the results of this study provide a theoretic and experimental evidence for clinical application of rh-IGF-1 in prevention and treatment of BPD.