IgA protease is a neutral endopeptidase elaborated by certain streptococci in the human oral cavity and colon. The enzyme is unusually specific in that its known substrate is human secretory IgA and serum IgA of subclass IgA1, which it cleaves at a hinge region pro thr peptide bond to yield intact Fcα and Fabα fragments. The authors here report that culture filtrates of three strains of Neisseria gonorrhoeae and 4 Neisseria meningitidis (serogroups A, B, C, and Y) all contain IgA protease activity. The organisms were grown 24 hr at 37°C in modified Difco GC broth and the filter sterilized concentrated supernatant fluids were tested for IgA protease activity using human colostral (secretory) IgA and myeloma IgA as substrate. The 7 organisms examined all produce IgA protease, yielding Fcα and Fabα from both types of IgA. As in the case of streptococcal IgA protease, the neissereal enzymes cleave only IgA1 subclass paraproteins, are inhibited by EDTA, and are unaffected by serum protease inhibitors. However, the neissereal Fcα and Fabα have a slightly different mobility on disc gel electrophoresis when compared to the streptococcal fragments. These data indicate that pathogenic neisseriae are among the restricted number of bacteria producing an enzyme specifically destructive to human IgA.