This thesis is a study of the nature of the immune complexes in renal biopsies and in the circulation in various kinds of glomerulonephritis. There may be differences in clearance of circulating immune complexes from the circulation, dependent on the class of immunoglobulins, and the complement components present in the complex. Thus some complexes may be rather selectivel y eliminated from the circulation, and may be preferentially deposited in glomeruli. I have compared the immunoglobulins complexed in renal biopsies and in the circulation in various forms of glomerulonephritis, and found the composition of deposited and circulating complexes to vary with different forms of glomerulonephritis.