Crystalline preparations of rat skin acid-soluble collagen are a complex of collagen and glycoprotein of noncollagenic nature. Heat denaturation of the preparation, treatment with urea and DS-Na result in decomposition of this complex. Proteins composing it differ in amino acid composition, the presence of -S-S-bonds, the amount of a carbohydrate component, electrophoretic mobility in polyacrylamide gel and solubility in acid medium. Differential salting out by various NaCl concentrations permits separating the acid-soluble collagen preparations into fractions containing and noncontaining the accompanying noncollagen component. d