Cytoskeletal and membrane proteins were isolated from respectively the urea-soluble and urea-insoluble fractions of the squid lens. The main cytoskeletal polypeptide has a molecular weight (63000) and an amino acid composition similar to those of vertebrate intermediate filament proteins, including mammalian lens vimentins. Intermediate filaments, and bundles thereof, were regenerated from the squid lens urea-soluble fraction upon removal of urea. The main membrane polypeptide of 140000 Mrhas an amino acid composition entirely different from that of the main intrinsic membrane protein of 26000 Mrwhich is found in all vertebrates. Although non-EDTA-extractable, the 140000 Mrsquid membrane polypeptide is best classified as extrinsic, since it has a high polarity (mainly acidic residues) and can be degraded completely upon trypsin treatment of squid lens membranes.