[en] Temperature relationships between the third-order elasticity moduli were calculated along with the baric derivatives of the second-order elasticity moduli of alkali metals. Use has been made of a pseudopotential model that offers a good description of all the lattice properties of these metals. It has been established that the third-order moduli show a weaker change with temperature than those of the second order. It has been pointed out that the anharmonic contribution to the banic derivative of the compression modulus is low, whereas it is considerable in the derivative of the shear modulus C. The experiment and its agreement with the theory is discussed