Optical methods open new horizons in studying magnetoelectric interaction in magnetically ordered crystals. In the present paper we shall report on some new optical effects observed in two model crystals: in antiferromagnetic Cr₂O₃ and in ferrimagnetic Y₃Fe₅O₁₂. In Cr₂O₃ we observed a nonreciprocal rotation or plane-polarized light induced by ac electric field applied along optical axis. The temperature variation of this rotation was found to differ substantially from that of magnetoelectric effect in a low-frequency range. New antiferromagnetic mechanism of nonreciprocal rotation was suggested to exist in an optical spectral range. In Cr₂O₃ a second order optical magnetoelectric effect was observed for the first time which was related to an antiferromagnetic domain switching. In Y₃Fe₅O₁₂ electromagnetooptical effects were observed mainly in the regions of domain wall movement and rotation of magnetization. Much better resolution was obtained in comparison to a low-frequency study of magnetoelectric interaction. A forbidden, linear in electric field, effect was observed in Y₃Fe₅O₁₂ and we relate it to crystal imperfections, which destroy the symmetry center.