The study of skin protein fractions obtained by salt fractionation indicates that collagen is associated to a greater extent with the ribonucleoprotein fraction than with the deoxyribonucleoprotein fraction. The gelatin derived from the ribonucleoprotein fraction following in vitro incubation of foetal lambskin in the presence of glycine-2-14C was appreciably radioactive. Pre-treatment of the skin with crystalline ribonuclease resulted in a marked inhibition of glycine incorporation into total gelatin. whereas crystalline deoxyribonuclease had little effect. It is therefore concluded that ribonucleic acid rather than deoxyribonucleic acid is associated with the biosynthesis of collagen.