Results of first observation and theoretical treatment of photorefractive optical nonlinearity (PN) in nematics are discussed. Possible ways for further increase of PN are pointed out. Those lie in decreasing luminescence quantum efficiency of the dye used and increasing the mobilises’ ratio of positive and negative ions induced by light. The influence of interface screening effects on PN is treated theoretically and the ways for obtaining exact results for bulk charge densities and fields are worked out.