Summary: Following immunization of Swiss Webster mice with sheep erythrocytes or Escherichia coli lipopolysaccharide antigens, γA antibody-releasing cells were detected by a modification of the localized hemolysis-in-gel technique. When purified rabbit anti-mouse γA immunoglobulin was added to spleen cell suspensions before plating and enumerating, augmented numbers of antibody-releasing cells were detected. These “γAPFC” were found following primary and secondary injections of both antigens and were specifically inhibited by γA myeloma protein.