The authors studied the lytic and agglutinating activity of H-antibodies against S. typhimurium. Sera containing H-antibodies proved to possess a distinct lytic activity expressed in the presence of a complement and caused by specific antibodies. In H-antibodies specific lytic activity (as per 1 agglutinating unit) was much weaker than in O-antibodies. A relatively low lytic action of H-antibodies was apparently associated with topography of corresponding antigenic determinants of the microbial cell which determined the low possibility of fatal injuries. In examination of H-bacteriolysins there was revealed the same regularity as noted in studying the O-bacteriolysins: reduction of the lytic activity of antibodies in hyperimmunization.