Basic blue 93. An alternative to the traditional myeloperoxidase stain.

This report describes the selective staining of lysosomes in cells of neutrophilic granulocytic origin by the azo textile dye basic blue 93. Used as a single agent aqueous stain after fixation, the dye stained lysosomes black. Stained in this way, lysosomes were sharply delimited and easily visualized. Large numbers of black-stained lysosomes occurred in immature granulocytes like promyelocytes and myelocytes. In more mature granulocytes like metamyelocytes, bands, and neutrophils, substantially fewer numbers of lysosomes were detected. In leukemic myeloblasts and promyelocytes stained with basic blue 93, variable numbers of black-colored lysosomes could be detected and usually paralleled the reactions for myeloperoxidase and Sudan black B in the same cells. As an alternative to the traditional stains for myeloperoxidase, basic blue 93 has several advantages, including simplicity of use, ability to stain aged specimens, and stability of the reaction product.