The insoluble collagen from methylcholanthrene induced sarcoma was isolated and characterized. It contains more glycine, hydroxyproline and acidic amino acids than normal connective tissue collagen. An anionic character of tumour collagen was stated (pI 6.1). No typical collagen subunits in this protein were found. The tumour collagen is strongly bound to acidic glycoprotein containing a significant amount of hydroxylysine. Such an insoluble complex is resistant to the dispersing action of EDTA. It dissociates during heating in concentrated urea.