The hormone human chorionic gonadotropin (hCG) serves to maintain the fetus during early pregnancy and regulate the onset of labor in late pregnancy. hCG also prevents Neisseria gonorrhoeae from developing invasive characteristics. Part of the beta subunit of hCG has an amino acid sequence similar to that of the hinge of human IgA1, which is the site of action of IgA1 proteases. This study examined the sensitivity of hCG to gonococcal IgA1 proteases, by means of autoradiography, immunoblotting, and RIA. hCG was cleaved in the beta subunit by the type 1 but not the type 2 IgA1 proteases of N. gonorrhoeae. hCG cleavage by gonococcal IgA1 proteases in vivo may increase the invasiveness of the pathogen and destroy its natural biologic activity, with major consequences for the fetus and the pregnancy.