AbstractDuring screening of tissues we observed binding of the amyloid stains Sirius Red F3BA and Sirius Supra Scarlet GG-CF by eosinophilic leukocytes in formalin-fixed and Zenker-fixed material; in Carnoy-fixed sections, only amyloid was stained. The Alkaline Congo Red reaction colored amyloid selectively—eosinophilic leukocytes remained unstained in all samples tested. Binding of eosin and of sirius dyes by eosinophilic leukocytes in tissues and inin vitrothrombi was abolished by deamination for 24 hours; binding of the sirius dyes by amyloid was not affected. These observations indicate salt-type linkages between the dyes and a strongly cationic component in eosinophilic leukocytes. The stainable material is apparently extracted during fixation in Carnoy's fluid.