Timed-pregnant rats at a gestational age of 14 days were exposed to 10% ambient oxygen (normobaric hypoxia) and compared to pair-fed animals of the same gestation and controls fed ad libitum. The lungs of the offspring were analyzed morphometrically and biochemically at day 21 of gestation after cesarean section. The hypoxic mothers and the pair-fed mothers showed similar diminution of weight gain and their fetuses showed growth retardation, more so in those of the hypoxic mothers. The lung volumes and weights were significantly different in the offspring of hypoxic and pair-fed mothers compared to those of mothers fed ad libitum. However, the lung volume and lung weight to body weight ratios were not different between groups, including pair-fed and hypoxic, and lung size was proportional to the amount of general growth segment in all. Morphometric analysis showed the volume proportion of saccular air, saccular wall, conducting airways, and nonparenchyma to be the same in each group. The gas exchanging surface areas were also the same. Dry lung weight, DNA, and protein per lung were decreased in the offspring of hypoxic mothers compared to the two other groups. The issue of whether the offspring of the hypoxic mothers should be regarded as having specific hypoplasia because of diminished cell number is discussed.