A meningococcal outer membrane vesicle (OMV) vaccine was prepared from two production strains designed to express three serosubtype-specific class 1 outer membrane proteins or PorA. The resulting hexavalent PorA OMV vaccine contained the serosubtypes P1.7,16; P1.5,2; P1.19,15; P1.7h,4; P1.5c,10; P1.12,13 and were used to immunize adult volunteers. A single immunization with two dosages, 7.5 and 15 micrograms of the individual PorAs, was studied. The vaccine was considered safe for further use. Approximately half of the volunteers demonstrated a fourfold increase in bactericidal antibody activity against six test strains expressing the specific PorAs when given the higher dosage. This bactericidal activity was found to be directed against PorA.