A hybridoma produced by the polyethylene glycol fusion of the NS-1 variant of the P3x63Ag8 BALB/c plasmacytoma to splenocytes harvested from a BALB/ c mouse immunized with whole gonococci was found to be producing antibody to a common region on gonococcal lipopolysaccharide (LPS). Enzyme-linked immunosorbent assay inhibition systems were established by utilizing this antibody, designated 3F11, and 100% inhibition occurred with both LPS and the LPSderived polysaccharides from each of the six prototype strains. Meningococcal LPS and LPS-derived polysaccharides partially inhibited the enzyme-linked immunosorbent assay, whereas similar preparations isolated from Escherichia coli 0:111, the J-5 mutant of this strain, and Salmonella minnesota Re595 failed MATERIALS AND METHODS Strains. Prototype strains representative of the six gonococcal LPS serotypes were obtained from our own collection. These were strain 1342 (serotype Gc,), strain 1291 (serotype GC2), strain 4505 (serotype GC3), strain 8551 (serotype Gc4), strain PID2 (serotype Gcs), and strain 3893 (serotype Gc6). Strain 4505r was also 751 on August 1, 2020 by guest http://iai.asm.org/ Downloaded from