ASL once developed in man after a streptococcal infection tends to decline gradually with the lapse of time. However, he may be infected again when exposed to another type of Group A streptococcus different from the type of the previous infection, since various antibodies to extra- and intracellular components of streptococci, except the type-specific antibody, are not responsible for the antibacterial immunity. Although the reinfection with the same type of Group A streptococcus has been generally con-sidered to be very unusual (Wannamaker, 1954; Lancefield, 1959), there are many types in Group A streptococci and prevalent types in a community have been shown to change from time to time (Schwentker et al., 1943; Coburn, 1949; Wannamaker, 1954; Fukumi and Kusama, 1958; Noguchi et al., 1962) . Thus, one may undergo repeated infections many times during his life, eventually resulting in wax and wane of the ASL amplitude.
In the preceding report (Kusama et al., 1962a), the mechanisms of the ASL response were investigated in scarlet fever patients from the onset of the disease to the stage of the maximum response. In the present studies, patients were examined at appropriate intervals after released from the hospital until one year after the onset of the disease. Some of them were shown to be reinf ected, and efforts were made to envisage the dynamics of fluctuation of ASL titers and how ASL is being maintained in a population.
