Finite deformations have a stress (&sgr;)–strain (&egr;) relation of the form &egr;=s′11&sgr; +&dgr;(s11&sgr;)2, wheres′11is an elastic compliance and &dgr; is a combination of second‐order and third‐order elastic constants. Tensile tests performed on bismuth whisker crystals oriented in the ⟨111¯⟩ and ⟨11¯0⟩ directions give &dgr;111¯=7.6±0.5 and &dgr;11¯0=0±0.3, respectively. Orientations are given in the rhombohedral system in which the angle between axes is approximately 57°.