The distribution of receptors for immunoglobulins of several different isotypes was examined for group A streptococcal isolates derived from skin and nasopharyngeal sites. Although human IgG-Fc receptor activity was a variable property of group A streptococci, found among 61% of all isolates tested, it was largely restricted to well-defined subpopulations. Human IgG-binding activity was observed among nearly all impetigo isolates examined. In addition, the expression of the class II M protein molecule (one of two broad antigenic classes of the major virulence factor) and opacity factor (a lipoproteinase) was almost invariably accompanied by human IgG binding, regardless of tissue site of infection. In contrast to class I impetigo isolates, class I nasopharyngeal isolates were relatively devoid of human IgG-binding activity. The data suggest that the presence or absence of human IgG-binding activity correlates with certain diseases caused by group A streptococci.