Specific high-titered arbovirus C'F antibody was obtained in mouse ascitic fluid. Primary and secondary immunization consisting of multiple closely spaced injections produced an autibody response similar to that found after one primary and one secondary injection, but resulted in higher-titered yet similarly specific reagents. Subcutaneous inoculation was shown to be more effective than intraperitoneal inoculation for primary immunization, whereas the reverse was true for secondary immunization. CF and HI antibody in hyperimmune asctic fluid was found only in the gamma G-immunoglobin region. AC activity was found in the 19S portion of the gamma globulin region of unheated ascitic fluid; it was heat stable when isolated from 7B gamma G-immunoglobulin and heat stable in their presence. Non-specific inhibitors in the HI testt were shown to be lipoproteins that were not associated with 19S and 7S globulins.