The Cell-Check? Viability/Cytotoxicity Kit for Fungi/Yeast combines a novel two-color fluorescent probe for fungi/yeast viability, Yeast stain, with a fluorescent fungal surface labeling reagent of a third color, Calcofluor? White M2R. Calcofluor is an ultraviolet–excitable dye that has long been used as a marker of fungal cell walls.? The Yeast stain is used to determine the metabolic activity of fungal cells by fluorescence microscopy or through other instrumental techniques. The assay kit can be used for detecting fungi in complex mixtures or in pure cultures.