Using recently published experimental data we calculated the piezoelectric response of rhombohedral 0.67Pb(Mg1/3Nb2/3)O-3-0.33PbTiO(3) monodomain single crystals along arbitrary directions. The calculations indicate that the value of the longitudinal piezoelectric coefficient along the  axis of the pseudocubic system ( axis of the rhombohedral system) of a monodomain crystal is close to the value determined experimentally along the same direction of a multidomain crystal with a so-called "engineered domain state." The results thus show that the large piezoelectric response in this material is dominated by intrinsic crystal lattice effects and that the multidomain state has a relatively minor effect (<20%). In addition, calculations predict a transverse piezoelectric coefficient >1900 pC/N for certain directions of the monodomain crystal. (C) 2003 American Institute of Physics.