Proteins are substances on which the organic composition and structure of the cell depends. The protein concentration of the crystallin lens is higher than that of any other organ of the body. This predominance of proteins in the lens' substance points clearly towards the cardinal role they play in the metabolism of this organ. The present review is concerned with the problem of protein chemistry of the lens and mainly with the determination of the amino acid composition of the lenticular proteins. Such determinations were made on the undivided total proteins or on the isolated individual proteins.