We shunted amniotic fluid from alternate gestational sacs into the maternal peritoneal cavity between 23 and 30 days gestation in fetal rabbits (full term, 31 days) to investigate the effect of oligohydramnios on surfactant apoprotein A (SP-A) expression by an immunohistochemical morphometric analysis. The amniotic shunt produced a significant decrease in the amniotic fluid volume (P < 0.02), as well as a reduction in the lung weight (P < 0.005) and lung/body weight ratio (P < 0.001), which indicated lung hypoplasia. These fetuses also showed a statistically significant reduction of SP-A expression, ie, SP-A-positive type II cells per unit area (P < 0.05), SP-A-positive type II cells/total cells ratio (P < 0.001), the percentage of SP-A-positive area per unit area (P < 0.005), and the SP-A-positive area/alveolar epithelium area plus the lung interstitium area ratio (P < 0.005). These results suggest that oligohydramnios significantly retards and modifies the structural growth and functional development of alveolar type II cells in SP-A expression. This animal model of hypoplastic lung in fetuses is thus considered to be useful in helping to further develop the treatment for hypoplastic lung.