The protein metabolism in four cases of hereditary sensory radicular neuropathy was studied through the electrophoresis and immunoelectrophoresis of the blood serum. A slight increase of the gammaglobulin content was found in all cases. The immunoelectrophoresis showed an absense of IgA in a case, a slight increase of IgG in all cases, and an absence of IgM in two cases and a marked decrease of this macroglobulin in two cases of the disease and in their healthy parents. Only two patients showed an increase of beta1 lipoprotein.