Acetylation, sulfation and phosphorylation induce binding of resorcin-fuchsin by glycogen, basement membranes, reticulum fibers, collagen, and other tissue structures containing polysaccharides as demonstrated by the periodic acid Schiff reaction. These structures do not stain with resorcin-fuchsin in control section without pretreatment. It is concluded that the binding of resorcin-fuchsin is due to the introduction of ester groups. Extraction procedures, designed to remove dyes held by salt-like or ionic linkage, indicate binding of resorcin-fuchsin by non-ionic bonds. According to data on the dyeing of the polysaccharide ester cellulose acetate in textile dyeing, cellulose acetate dyes are adsorbed by hydrogen-bonding between the carbonyl oxygen of the ester group and phenolic hydroxyl groups of the dye. It seems possible that in resorcin-fuchsin a phenolic hydroxyl group of the resorcinol moiety of the dye is free to react. The intense staining of agar, esterified glycogen, collagen and reticulum fibers with resorcin-fuchsin implies that binding of this dye does not convey any information concerning the protein moiety of tissue structures. Thus, resorcin-fuchsin can not be considered specific for elastic fibers in the chemical sense of the term.