Bismuth (Bi) stains nucleoproteins (NPs) by interacting with available amino and primary phosphate groups. These two staining mechanisms are distinguishable by glutaraldehyde crosslinking (Fig. 1,2).Isolated mouse liver nuclei, extracted with salt and acid solutions, fixed in either formaldehyde (form.) or gl utaraldehyde (glut.) and stained with Bi, were viewed to determine the effect of the extractions on Bi stainina. Solubilized NPs were analyzed by SDS-polyacrylamide gel electrophoresis.Extraction with 0.14 M salt does not change the Bi staining characteristics (Fig. 3). 0.34 M salt reduces nucleolar (Nu) staining but has no effect on interchromatinic (IC) staining (Fig. 4). Proteins responsible for Nu and glut.- insensitive IC staining are removed when nuclei are extracted with 0.6 M salt (Fig. 5, 6). Low salt and acid extraction prevents Bi-Nu staining but has no effect on IC staining (Fig. 7). When nuclei are extracted with 0.6 M salt followed by low salt and acid, all Bi-staining components are removed (Fig. 8).