Determining the profile of antigen expression among meningococci is important for epidemiologic surveillance and vaccine development. To this end, two new mouse monoclonal antibodies (MAbs) have been derived against Neisseria meningitidis proteins (class 5). The MAbs were reactive against outer membrane antigens and were bactericidal. Selected anti-class 5 MAbs [(5.1)-3E6-2; (5.3)-3BH4-C7; (5.4)-1BG11-C7; (5.5)-3DH-F5G9 also 5F1F4-T3(5.c)], and the two new monoclonal antibodies C14F10Br2 (5.8) and 7F11B5Br3 (5.9), were then tested against different meningococcal strains, (63 strains of serogroup A, 60 strains of serogroup C (from 1972 to 1974); and 136 strains of serogroup B (from 1992) meningococci). Our results demonstrated that the expression of class 5 proteins in the N. meningitidis B Brazilian strains studied is highly heterogeneous. The serotypes and subtypes of B:4:P1.15, B:4:P1.9, B:4:P1.7, B:4:P1.3, B:4:P1.14, B:4:P1.16, B:4:NT, and B:NT:NT were detected in N. meningitidis B serogroups. The strains C:2a:P1.2 and A:4.21:P1.9 were dominant in the C and A serogroups, respectively. Serogroup B organisms expressed the class 5 epitopes 5.4 (18%), 5.5 (22%), 5.8 (3.6%), 5.9 (8.0%) and 5c (38%). Serogroup C expressed class 5 epitopes 5.1 (81%), 5.4 (35%), 5.5 (33%) and 5.9 (5.0%); and serogroup A showed reactivity directed at the class 5 protein 5c (47%); and reactivity was present with the new monoclonal antibody, 5.9 (5.5%). We conclude that the two new MAbs are useful in detecting important group B, class 5 antigens, and that a broad selection of serogroup B, class 5 proteins would be required for an effective vaccine based on the class 5 proteins.