An indirect enzyme-linked immunoassay (ELISA) has been developed to analyze the antigenic profile of the outer membrane serotype complex of Neisseria gonorrhoeae. Antisera raised in rabbits to serotype-specific vesicles (SSV) reacted primarily with homologous SSV; however, there was significant cross-reactivity (less than 50%) with heterologous SSV. N. meningitidis SSV cross-reacted with all antigonococcal SSV but at a lower degree (less than 20%). Preimmune sera did not cross-react significantly with all antigonoccoccal SSV. The sensitivity of the ELISA was enhanced when the integral SSV proteins 1a and 2 were used as adsorbed antigen. Heterologous anti-SSV cross-reacted slightly, having ELISA values less than 15% of the homologous reaction. Antisera prepared by immunoabsorbent affinity columns were highly specific. Homologous affinity anti-SSV reacted only with proteins 1a and 2. The reaction of immune sera was inhibited by homologous proteins 1a and 2; lipopolysaccharide and proteins 1a and 2 isolated from heterologous serotypes did not inhibit the reaction. The reaction of affinity-purified antisera could be inhibited only by homologous protein 1a. By the use of affinity-purified antisera, a specific and highly sensitive ELISA was developed to analyze the antigenic profile of strains of N. gonorrhoeae.