A procedure to prepare and maintain bovine fetal lung (BFL) cell cultures was established. These cell cultures grew abundantly and readily and were easy to handle. Monolayers could be kept in satisfactory condition in maintenance medium for 14 days. The yield from the lungs of one fetus was 15 to 30 primary culture Roux bottles, and 40,000 5th-generation test tubes. The BFL cells were satisfactorily kept at minus 70 C with the addition of dimethyl sulfoxide (DMSO). When the BFL cell cultures were infected with cytopathic bovine viral diarrhea (BVD) viral strains, the cytopathic effect (CPE) was clear and distinct and was first seen on postinoculation (PI) day 1. The end points for viral titrations and serum-neutralization (SN) tests were readily determined. The BFL cells were satisfactory for supporting replication of the BVD viral strains. The titer of the virus propagated in the cells was 10-7.0 to 10-8.0 median tissue culture infective doses (TCID50)/1ML. Growth curves of the BVD viruses are reported.