A series of transfusion studies has been performed, in which either plasma or plasma together with peripheral leukocytes has been transfused from patients with rheumatoid arthritis into non‐rheu‐matoid recipients. The donors of the plasma and leukocytes all had very high levels of rheumatoid agglutinating activity. There was no indication in these studies that transfusion of the rheumatoid factor complex has had ability to produce disease in the recipients; at least under the conditions of these experiments. In a two to three year follow‐up after these transfusions, there was still no evidence of development of disease in the recipients.