Protein fractions of low molecular weight from urines of patients with tubular proteinuria were separated by gel filtration. Their composition was studied by electrophoresis and immunoelectrophoresis.

Antisera raised against cerebrospinal fluid, urinary proteins, and extracts from human brain and subarachnoid cysts were absorbed with normal human serum and plasma, and employed to develop precipitin lines corresponding to trace components of CSF, urines, and extracts from brain and kidney. Several of these trace components were identified in more than one tissue or fluid. The site of origin is discussed for some of them.

Cerebrospinal fluid (C.S.F.) proteins have been analyzed by immunoelectrophoresis, using rabbit anti-C.S.F. antiserum absorbed with normal human serum, 9 precipitin lines were thus demonstrated. One of these C.S.F. proteins (“post-γ” or “X-γ”) was studied in more detail and proved to have an electrophoretic mobility essentially dependent upon the conditions of storage of the C.S.F. samples. The presumed identity of this component with C.S.F. protein fractions described in the literature is discussed.