Antigens that determine agglutination reactions, and are distinct from the O-, H- and Vi-antigens, were demonstrated in the type-1 fimbriae of bacteria in fimbriate-phase cultures of salmonellae. Most strains of salmonellae produced fimbriate cultures when grown for a sufficient period, e.g., 24–48 hr, at 37°C in aerobic static broth. The same strains produced non-fimbriate-phase cultures lacking fimbrial antigens when grown for only 6 hr in broth, for 12 hr in glucose broth or for 24 hr on an agar plate. The independence of the fimbrial antigens from the O-, H- and Vi-antigens was shown by the finding that an antiserum raised against a fimbriate-phase culture and freed from O-, H- and other non-fimbrial agglutinins by absorption with non-fimbriate-phase bacteria (“pure fimbrial antiserum”) strongly agglutinated fimbriate-phase bacteria, but did not agglutinate either non-fimbriate-phase bacteria or fimbriate bacteria that had been defimbriated by heating at 100°C.