Gravid mice become progressively more susceptible to infection with the pancreatic line of Group B-1 Coxsackie virus during the last week of pregnancy. A Group A-8 strain did not have such an effect. The young that survive despite the fact that their mothers are infected with a B-1 strain appear to be normal in the gross and microscopically, to grow at the usual rate, to be free of demonstrable virus, and to be susceptible on challenge with a homologous strain.