Abstract: A monitoring technique for use in the regeneration of spent bleach-fix solution containing silver ion and ferrous ion resulting from photograhic processing. Regeneration comprises first treating the spent solution with elemental iron to reduce and chemically replace silver ion, and thereafter dispersing an oxidizing agent throughout the silver-free solution to convert ferrous ion to ferric ion. Exhaustion of the elemental iron in the silver replacement step or insufficient oxidation in the ferrous-ferric conversion step are electrochemically detected by comparison of the half-cell potential of a reference solution drawn from the bleach-fix solution in a region of the regenerative cycle where the solution is substantially insensitive to the exhaustion of the elemental iron and insufficient oxidation. Further provision of a continuously flushing reference solution provides longterm accuracy of the electrochemical monitoring method.