Summary: Information has been presented which proves that the antipoliovirus activity in human milk is specific antibody. Milk has also been found to contain neutralizing antibodies for coxsackie- and echoviruses and probably for the virus of herpes simplex. In spite of immunoelectrophoretic and chromatographic differences between the antibodies in milk and serum, data from the present study would indicate that the immune globulin molecule in each case may contain very similar, if not identical, antibody combining sites for polioviruses.