PLATES 1 TO 4(Received for publication, July 20, 1960.)The present work gives evidence by use of fluorescent antibody methods of deposits of bound gamma globulin with characteristic histologic distribution in the auricular appendages of certain patients with rheumatic heart disease. These deposits were not associated with Aschoff lesions; they occurred in spotty distribution throughout the myocardium, involving myofibers, and to a lesser extent, connective tissue and vessel walls. Other proteins, i.e., albumin and fibrinogen, were absent from these foci. Furthermore, the tissue sites demonstrating fixation of gamma globulin frequently exhibited evidences of alteration as indicated by affinity for eosin and intense reactivity with the periodic acidSchiff stain. Bound gamma globulin with associated histochemical change was observed in a significant proportion of rheumatic hearts, but not in normal or pathologic control tissues.In previous studies of rheumatic hearts, Vazquez and Dixon (1) described in fixed tissue sections gamma globulin in altered perivascular connective tissue and in Aschoff lesions. According to the authors, "it was not possible to show a difference between the amount of gamma globulin visualized specifically within the fibrinoid necrosis of the Aschoff bodies and in the immediate