A reaction is described between some streptococci and IgA myeloma proteins; most streptococci showed low affinity for IgA myeloma proteins, with the exception of group A, type M 4 and two freshly isolated group A streptococci; they took up 40 to 50 per cent of 1 μg 125I labelled IgA myeloma protein added. Addition of similar amounts of unlabelled IgA and IgG myeloma proteins showed no cross inhibition between uptake of IgG and IgA. Heat- and trypsin treatment of the streptococci did not reveal any differences in IgA and IgG reactivity. The uptake of one 125 I labelled IgA myeloma protein was inhibited uniformely by four randomly selected unlabelled IgA myeloma proteins. Thus, the uptake of 125 I labelled IgA myeloma protein seems to be independent from the specificity of the antibody combining sites.