Six gilts were inoculated intramuscularly with 2.5×106 tachyzoites of Neospora caninum on three different days of gestation to study the pathogenic effect of Neospora infection in pigs, including possible transplacental transmission. The gilts were euthanized 59, 30, and 9/10 days postinoculation (p.i.), corresponding to days 107, 102/106 and 110/111 of pregnancy. With the exception of one animal (euthanized day 9 p.i.) all gilts seroconverted as measured by the indirect, fluorescent antibody test (IFAT). Neosporosis with multifocal intralobular necrotizing hepatitis was seen in the two gilts inoculated 9/10 days before euthanasia. The uterus of one gilt inoculated 59 days before euthanasia revealed granulomatous and focal necrotizing endometritis with a corresponding multifocal necrosis of the trophoblasts of two fetuses. Transplacental neosporosis was indicated in the two fetuses by strongly elevatedNeospora IFAT titres in pleural fluid and by the presence of multifocal necrotizing encephalitis and hepatitis together with non-suppurative myocarditis, pneumonitis, nephritis and hepatitis. Furthermore, N. caninum was re-isolated in cell culture from one of these fetuses. A third fetus from the same gilt revealed only disseminated, pinpoint necroses in the liver. Immunohistochemically, N. caninum tachyzoites were detected in association with histopathological changes in the liver and the endometrium of the gilts, and in the brain, liver, and allantochorion of the three fetuses.