An immunoglobulin distinct from IgG and IgM has been identified in chicken serum, intestinal secretions, and bile (1). Its homology with mammalian IgA was inferred from the antigenic individuality of its heavy chains and its high concentration in two exocrine secretions, viz, intestinal juice and bile. The present communication deals with the distribution of the three immunoglobulins, IgG, IgM and IgA in the spleen and intestinal mucosa of five adult conventional chickens. Specific antisera gainst γ, µ and α chains (1) were labeled with fluorescein isothiocyanate according to standard procedures (2). Tissue samples were processed to 5-µ sections in a Cryo-Cut microtome (American Optical Corporation), incubated with the labeled antisera and examined under ultraviolet light for immunoglobulin-containing cells. In the spleen (Fig. 1), plasma cells were predominantly distributed around the germinal centers and most of these cells stained with anti-γ or anti-µ reagents. Only few cells reacted with anti-α.