An improved method of determining the collagen and elastin in uncooked animal tissues is described, and its accuracy is measured and discussed. The results of its application to beef muscle from carcasses of definite antecedents and description are given. No constant and significant differences in connective tissue content were found between heifer and steer beef. Among different retail cuts of beef examined, the eye-muscle of the rib possessed for practically all calves examined the lowest content of collagen, expressed as collagen nitrogen in per cent of total nitrogen. The tenderloin was only slightly higher. The round, porterhouse and sirloin were next in order and were indistinguishable from each other in this respect. The chuck ribs and the navel contained consistently larger percentages of collagen nitrogen than the more expensive cuts, but the fore shanks of all calves contained the highest, the collagen nitrogen of this cut averaging 23 per cent of the total nitrogen of the lean. The outer round generally contained more collagen than the inner round. The percentage of elastin in muscle is only a small, in most cases an insignificant, fraction of the percentage of collagen. The distribution of elastin among the different retail cuts of meat differs from the distribution of collagen, but appears to be as consistent and as significant. Age does not seem to have a great effect upon the connective tisse content of muscle meat, nor a consistent effect among the different muscles of the carcass. However, much of the data obtained on this point were so irregular as to preculde any definite conclusions. No relation at all was noted between the ordinary market grading of beef carcasses and the connective tissue content of the lean of the rib (eye) or of the round. Insofar as the tenderness of meat is related to its content of connective tissue, the results obtained in this investigation lend no support to the belief that the appearance, texture and firmness of its lean gives reliable information concerning its tenderness. No obvious relation was found between the grading of beef carcasses and the fat content of the lean of selected samples.