Squid mantle was treated with probes to establish the relative importance of collagen and contractile proteins in tensile strenght as a function of sample orientation. Collagenase was used to modify collagen, and NaCl and a crude trypsin preparation were used to modify the contractile elements. The results support the hypothesis that collagen is a primary determinant of raw mantle strenght in the longitudinal direction and that muscle fibers are relatively more important in the transverse