Monoclonal antibody technologies were applied to the study of early events in porcine parvovirus (PPV) infections in vitro. Balb/c mice were immunized with whole swine testicle cells and hybridomas were produced following fusion with myeloma cells. Resultant clones were screened firstly in an ELISA system, to detect monoclonal antibody recognition of swine testicle cells, and secondly, in a fluorescent antibody test to detect monoclonal antibody which inhibited production of PPV antigen. One clone, 1H11, which satisfied these screening requirements, recognized proteins present in cell lines both permissive and non-permissive for porcine parvovirus replication and inhibited the production of virus progeny of several PPV isolates. A linear staining pattern of cross-linked plasma membranes, indicative of monoclonal antibody binding at the cell membrane, was demonstrated by indirect immunofluorescence assays. In immunoblotting experiments, 1H11 recognized a polypeptide of approximately 40 kDa in size, present in both permissive and non-permissive cell lines.