An electron spin resonance signal has been observed in Li-doped ZnO crystals after UV illumination at 77°K. The spectrum has axial symmetry around the c-axis of the hexagonal crystal and shows for H ⊥ c a well resolved quartet pattern because of an interaction of the unpaired spin with a Li7 nucleus. The responsible center is probably a hole, trapped predominantly on that oxygen ion, nearest to a substitutional Li+, which is in the direction of the polar c-axis of the ZnO crystal. The intensity of the esr-signal could be quenched or enhanced by subsequent illumination with visible or infrared light. This effect was usually accompanied by charge transfer processes between the lithium center and iron impurities.