Recombinant Norwalk virus-like particles (rNV VLPs) were administered to BALB/c mice by the intranasal (i.n.) route to evaluate the induction of mucosal antibody responses. The results were compared to systemic and mucosal responses observed in new and previous studies (J. M. Ball, M. E. Hardy, R. L. Atmar, M. E. Connor, and M. K. Estes, J. Virol. 72:1345-1353, 1998) after oral administration of rNV VLPs. Immunizations were given in the presence or absence of a mucosal adjuvant, mutant Escherichia coli heat-labile toxin LT(R192G). rNV-specific immunoglobulin G (IgG) and fecal IgA were evaluated by enzyme-linked immunosorbent assay. The i.n. delivery of rNV VLPs was more effective than the oral route at inducing serum IgG and fecal IgA responses to low doses of rNV particles. Vaginal responses of female mice given VLPs by the i.n. and oral routes were also examined. All mice that received two immunizations with low doses i.n. (10 or 25 microg) of rNV VLPs and the majority of mice that received two high doses orally (200 microg) in the absence of adjuvant had rNV-specific serum IgG, fecal, and vaginal responses. Additional experiments evaluated whether rNV VLPs can function as a mucosal adjuvant by evaluating the immune responses to two soluble proteins, keyhole limpet hemocyanin and chicken egg albumin. Under the conditions tested, rNV VLPs did not enhance the serum IgG or fecal IgA response to these soluble proteins when coadministered by the i.n. or oral route. Low doses of nonreplicating rNV VLPs are immunogenic when administered i.n. in the absence of adjuvant, and addition of adjuvant enhanced the magnitude and duration of these responses. Recombinant NV VLPs represent a candidate mucosal vaccine for NV infections in humans.