Pharmacological properties of the "Skin Reactive Factor" demonstrated in nephrotic patients are similar to guinea-pig Skin Reactive Factor. This biological activity is not antagonized by anti-histaminic and anti-serotonin drugs. It is inhibited by meclofenamate and pyridinolcanbamate. It is enhanced by diethyldithiocarbamate and normal human serum. According to this results it could be an activator of the kinin system. Biochemical studies indicate that it is a pepsin destroyed protein, unaffected by Rnase and Dnase. Its electrophoretic mobility is that of an albumin or an alpha1 globulin.