The complete sets of elastic constants of 4H and 6H silicon carbide single crystals were determined by Brillouin scattering. The elastic constants of 6H SiC areC11=501±4,C33=553±4,C44=163±4,C12=111±5,andC13=52±9 GPa;the corresponding ones of 4H SiC are the same within experimental uncertainties. The compressibility,4.5×10−3 GPa,is about 3–5 times smaller than those reported for polycrystalline SiC materials. ©1997 American Institute of Physics.