1. Glomerular permeability to protein and dextran was studied in four patients with bleeding disorders who had normal renal function and in whom proteinuria occurred during the large infusions of plasma needed for treatment of the primary disorder.
2. Results are expressed in terms of selectivity indices which relate clearance to molecular weight.
3. Dextran selectivity was high both in the presence and absence of proteinuria and protein selectivity during proteinuria was also high.
4. Proteinuria induced by plasma infusion is likely to be glomerular in origin and the results indicate that the normal glomerulus is highly selective to plasma protein as well as to dextran.