A photoconductive signal has been observed in ZnO single crystals at 300°K upon illumination with the 6935‐Å laser light from a ruby rod. With a dark current of 2 mA, a typical peak increase in current was 7 &mgr;A.Green luminescence (centered at 5250 Å) excited by the laser light was also detected. The fluorescent intensity showed an approximately second‐power dependence on incident intensity at lower intensities. At higher intensities an approximately fourth‐power dependence was noted. A plausible model is given to account for the second‐ and fourth‐power dependencies in terms of a two‐photon absorption mechanism. Since the absorption coefficient of ZnO for light of wavelength 6935 Å is quite small, the observed photoconductivity and luminescence are very likely associated with the bulk rather than with the surface.