Among a group of four selected strains ofNeisseria gonorrhoeae, common and strain‐specific antigens were demonstrated by immunoelectrophoresis, indirect immunofluorescence (IFL) and co‐agglutination (COA). In preparations of ultrasonically‐disrupted organisms, the strain‐specific antigens appeared in crossed‐line immunoelectrophoresis (C‐LIE) with antigen containing intermediate agar get as a two‐peak precipitin line, one peak close to the antigen well, the other towards the anode. A similar pattern was found for each of the four strains studied. These strain‐specific precipitin lines were also identified in rocket‐line immunoelectrophoresis (R‐LIE) tests, which were found useful for comparative studies. Using whole cells, strain‐specific antigens were also demonstrated by COA and IFL tests with the use od cross‐absorbed antibodies. The results corresponded to those obtained with C‐LIE and R‐LIE. Immunosorption experiments indicated identity between the strain‐specific antigens shown by COA tests and those demonstr