A method to evaluate the efficacy of bovine viral diarrhea virus (BVDV) vaccines using a multiple challenge model was investigated. Four pregnant heifers were challenged intranasally with a type I and type II isolate of BVDV at 75 days of gestation. At 60 days postinoculation, virus isolation and RT-PCR from blood and tissues of fetuses indicated that all fetus were persistently infected with both type I and type II isolates. Differing results of detection by PCR and virus isolation between the type I and type II isolates were obtained. These preliminary studies may indicate differences in the level of replication between type I and type II BVDV as well as predilected sites of replication in certain tissues.