Effect of nebulized 25D and 1,25D on lung morphometry. 2 weeks of daily administration of 25D (100 ng/kg) and 1,25D (1 ng/kg) from postnatal day 0 to 14 resulted in increased alveolarization, as determined by the alveolar count and mean linear intercept; mean alveolar count increased significantly (11.2 ± 1.1, 14.1 ± 1.3, 13.7 ± 0.8; control, 25D, and 1,25D groups, respectively under ×10 magnification: *p < 0.05 vs. control for both 25D and 1,25D groups), while mean linear intercept decreased significantly (25.9 ± 2, 21 ± 1.8, 22 ± 1.9 μm; control, 25D, and 1,25D groups, respectively under ×10 magnification: *p < 0.05 vs. control for both 25D and 1,25D groups). n = 6