INTRODUCTIONStaining yeast cells for the presence and localization of antigens has been particularly challenging because of several factors. The yeast cells are small, making the resolution of any antigen difficult; they have a thick cell wall that antibodies cannot penetrate and that is difficult to remove; and they grow in suspension, making handling difficult. Background problems can be especially severe, particularly with polyclonal antibodies, because many antisera contain antibodies to yeast cell-wall components. The difficulties encountered in localizing antigens in yeast can be overcome by using fluorochrome-labeled secondary antibodies, controlled enzymatic removal of the cell wall, and by binding the cells to a solid phase (e.g., poly-L-lysine-coated slides).