Niagara sky blue 6B--a new stain for granulocytic cells.

Using an acidified solution of Niagara sky blue 6B, granules in mature granulocytic cells from peripheral blood and bone marrow stained bright blue to blue-green. Granules in immature granulocytes like myelocytes and promyelocytes stained purple. In leukemic myeloblasts and leukemic monocytes, granular-appearing structures stained purple. In leukemic lymphoblasts, purple granular structures were not visualized. As such, Niagara sky blue 6B can be used to identify granulocytic cells at all maturational stages.