Photoinduced changes of the concentration of paramagnetic and optical defects have been investigated in cubic stabilized zirconia single crystals by means of electron paramagnetic resonance (EPR). Results are reported confirming the presence of photobleaching of the optical and EPR ${\mathrm{Zr}}^{3+}$ electron centers (T centers) in x-ray-irradiated crystals, but showing at the same time the photoproduction of ${\mathrm{O}}^{\mathrm{\ensuremath{-}}}$ hole centers. These data bring evidence of the complex mechanism of ${\mathrm{Zr}}^{3+}$-${\mathrm{O}}^{\mathrm{\ensuremath{-}}}$ annihilation, allowing a possible interpretation of the process. \textcopyright{} 1996 The American Physical Society.