The contribution of stilbene-parahydroquinone structures, formed from &bgr;-5 units during refining and bleaching, in photoreversion of peroxide-bleached high-yield pulps, was studied using 4'-benzyloxy-2,5-dihydroxy-3,3'-dimethoxystilbene (I), as a model compound. The various photoproducts formed during irradiation ofIin solution or adsorbed on cellulose paper were identified. Isomerization of the stilbene double bond and oxidation of the hydroquinone into quinone were observed in solution, whereas in the solid state only the formation of the quinone was found to operate. Our attempts to detect and quantify stilbene-hydroquinones forming from &bgr;-5 units created on peroxide bleached mechanical pulp were not met with success.Key words: lignin, stilbene, hydroquinone, lignin model compound, pulp, photoyellowing.