Recent developments in our understanding of cellular hypersensitivity indicate that antibody formation and cellular hypersensitivity commonly accompany each other and that a purely humoral or cellular response is most often an exceptional product of either an abnormal immunologic system or an unusual mode of immunization. Thus, the finding of Rocklin et al. (page 497) that cellular hypersensitivity may accompany the formation of antibody reactive with glomerular basement membrane (GBM) is not unexpected, particularly since GBM or BM antigens are present in both serum and urine of normal and nephritic humans and readily available to all types of immunocompetent cells.¹ This . . .