ZnO microwires grown by carbothermal reduction were mechanically bent and the uniaxial stress state was studied with spatially resolved low-temperature photoluminescence. Inhomogeneous (tensile and compressive) stress (up to +/- 1 GPa) is visualized by the redshift and blueshift of the wire luminescence. Experimentally determined tensile and compressive strain along the c-axis (wire axis) of up to 1.5 %, symmetrically distributed with respect to the central axis (neutral fiber), is achieved, resulting in maximum energetic shifts of +/- 30 meV. Within these experiments, we are able to precisely determine the direct relation between energetic shift of the free A-exciton energy and strain to (-2.04 +/- 0.02) eV. (C) 2011 American Institute of Physics. [doi:10.1063/1.3544939]