Pregnant ferrets were inoculated intra-cardially on day 30 of gestation with influenza virus. The animals were sacrificed on days 5 to 11 after inoculation and the products of conception including the uterus were examined virologically and histopathologically. The results indicate that the initial site of infection of the conceptus is the haemophagous organ and that spread occurs from this site to the endometrium, placental labyrinth and fetus. Lesions in the fetus are confined to the liver and respiratory tract. In the liver they may represent either a viral hepatitis or a secondary response to placental damage resulting in the stimulation of erythropoiesis. In the respiratory tract they first occur in the nasal sinuses and upper airways suggesting that infection is via the amniotic fluid rather than via the blood stream. The relevance of these findings to human pregnancy is discussed.