Various monoclonal antibodies (MAbs) that recognize cell surface proteins on bovine cells were previously shown to efficiently block infection with bovine viral diarrhea virus (BVDV) (C. Schelp, I. Greiser-Wilke, G. Wolf, M. Beer, V. Moennig, and B. Liess, Arch. Virol. 140:1997-2009, 1995). With one of these MAbs, a 50- to 58-kDa protein was purified from calf thymus by immunoaffinity chromatography. Microchemical analysis of two internal peptides revealed significant sequence homology to porcine and human CD46. The cDNA of bovine CD46 (CD46bov) was cloned and further characterized. Heterologously expressed CD46bov was detected by the MAb used for purification. A putative function of CD46bov as a BVDV receptor was studied with respect to virus binding and susceptibility of nonpermissive cells. While the expression of CD46bov correlated well with the binding of [3H] uridine-labeled BVDV, the susceptibility of cells nonpermissive for BVDV was not observed. However, the expression of CD46bov resulted in a significant increase in the susceptibility of porcine cells to BVDV. These results provide strong evidence that CD46bov serves as a cellular receptor for BVDV.