Monoclonal antibodies (MAbs) are important for in-depth antigenic characterization and diagnosis of infections with human caliciviruses that cause almost all outbreaks of nonbacterial gastroenteritis. We compared different routes of immunization with nonreplicating virus-like particles (VLPs) from recombinant Norwalk virus (rNV) and recombinant Mexico virus (rMX) administered to BALB/c mice to determine the efficiency of hybridoma production. Oral immunization with VLPs without adjuvant resulted in high yields of MAb-secreting hybridomas (90%) to these VLPs of IgG (61%), IgM (29%) and IgA (10%) isotypes. Fusions with mesenteric lymph node lymphocytes yielded MAbs of various subclasses including IgG2a, IgG3, IgM and IgA. These results suggest that an immunization route that mimics the natural route of viral infection pathway may facilitate MAb technology by increasing the yields of antibody secreting hybridoma cells.