The transverse piezoelectric coefficient (d(31)(star)) has been calculated for tetragonal barium titanate (BT) and lead titanate (PT) cut along nonpolar axes, over a range of temperatures, using the phenomenological Landau-Ginzburg-Devonshire theory. It is shown that negative values of d(31)(star) are favored when the transverse dielectric susceptibility eta(11) and shear coefficient d(15) are large, such that polarization rotation is more significant than the collinear piezoelectric effect. This occurs in tetragonal BT close to its ferroelectric-ferroelectric phase transition to an orthorhombic phase. In PT, however, where no phase transition occurs, d(15) is small and polarization "extension" due to d(33) dominates: small or positive values of d(31)(star) become prominent. This extends a previous result found for polycrystalline modified PT ceramics. (c) 2005 American Institute of Physics.