AbstractThe possible role of placental pathology in teratogenesis has not been fully understood. Since cyclophosphamide is a proven teratogen, it was decided to investigate its effect on placental histology. A single dose of cyclophosphamide (20 mg/kg) administered to pregnant rats on day 12 of gestation resulted in various malformations and stunting of fetuses at term. The placentae were significantly (P<0.001) lighter and their margins contained a patch of necrotic substance. The decidua basalis showed dilatation of blood spaces, hemorrhage and infarction. Giant cells were numerous and the glycogen cells sparce in the basal zone. Vast areas of infarction and necrosis were also evident here. The labyrinths were shorter and often hyalinised. In two cases cysts of considerable size occupied the centre of the labyrinthine zone. The necrotic patch was found to be fibrinoid in nature with and without the association of large giant cells and lymphocytes.