This paper describes a method for the specific histochemical demonstration of antibody using a two-stage immunological reaction on frozen tissue sections. The first stage involves allowing the tissue to react with a dilute antigen applied in vitro, followed by the detection of specific antigen absorption using fluorescein-labeled antibody. This method reveals yellow-green fluorescence in areas where a precipitate has formed, indicating the presence of antibody. The study focuses on hyperimmune rabbits and finds that antibody is present in groups of plasma cells in the red pulp of the spleen, medullary areas of lymph nodes, submucosa of the ileum, and portal connective tissue of the liver. Non-specific reactions are common, particularly in the bone marrow, and small amounts of antibody are occasionally detected in lymphoid follicles. The method confirms that plasma cells are the major site of antibody formation and provides insights into the cellular changes associated with immune responses.This paper describes a method for the specific histochemical demonstration of antibody using a two-stage immunological reaction on frozen tissue sections. The first stage involves allowing the tissue to react with a dilute antigen applied in vitro, followed by the detection of specific antigen absorption using fluorescein-labeled antibody. This method reveals yellow-green fluorescence in areas where a precipitate has formed, indicating the presence of antibody. The study focuses on hyperimmune rabbits and finds that antibody is present in groups of plasma cells in the red pulp of the spleen, medullary areas of lymph nodes, submucosa of the ileum, and portal connective tissue of the liver. Non-specific reactions are common, particularly in the bone marrow, and small amounts of antibody are occasionally detected in lymphoid follicles. The method confirms that plasma cells are the major site of antibody formation and provides insights into the cellular changes associated with immune responses.