Experimental work on the restoration of discoloured photographic prints carried out during the last few years at the National Archives of Canada is described. The mechanism of deterioration of the image-forming silver grains was also examinated. Emphasis was placed during restoration experiments on careful monitoring of the effect of the various chemical reagents on the morphology of the photograph. Restored photographic prints display improved stability characteristics because of the final treatment step in a selenium toning bath. The procedure used is not universally applicable to all paper prints and its restriction should therefore be clearly understood. Colour, B/W photographs, tables, diagrams, references.