Improved polychrome staining of 1-1.5 mum epoxy sections is achieved with sequential applications of a single basic fuchsin-methylene blue mixture at two different pH values. The dye solution is applied for 2-3 min at 50-52 C first at pH 7.9, then at pH 6.7. In sections of mouse mammary tissue, epithelial cells are stained deep blue, connective tissue pink, and fat cells bright olive-green. This simple technique consistently yields uniform, vivid, contrasting colors that sharply delineate the elements of the complex glandular architecture of the mammary gland. Similar polychromatic effects are obtained in applications to other tissues, such as stomach, adrenal gland, mammary tumor and artery.