An anti-idiotope monoclonal antibody (MAb), called CA1 (Ab2), was produced in mice against MAb 2C7, which recognizes a widely in vivo-expressed gonococcal lipooligosaccharide (LOS) epitope. Mice immunized with MAb CA1 initially had a 2.5-fold increase in IgG (12-fold after a booster) but no increase in IgM anti-LOS (Ab1') antibody. Control mice immunized with LOS had a 4.5-fold rise in IgG and 4-fold rise in IgM anti-LOS antibody. In rabbits, MAb CA1 elicited a 9-fold rise in IgG and a 3.3-fold rise in IgM anti-LOS (Ab1') antibody. Ab1' antibody bactericidal activity was 1-2 logs greater than that produced by immunization with LOS. Ab1' mediated complete human polymorphonuclear leukocyte phagocytosis of 2C7 epitope-positive (but not 2C7 epitope-negative) gonococci. MAb CA1 acts as a molecular surrogate (Ab2beta) for the nominal LOS antigen and may form the basis for vaccine candidates for human immunization against Neisseria gonorrhoeae.