In forced aging tests of Cibachrome images up to 300 days at 40% RH, 77 and 85°C, density losses remain at less than 5% for the three dyes. At 60% RH, 70 or 85°C, a noticeable change after 112 days is observed. The absorption spectra show that a change in the aggregation stage of the dyes takes place. This deaggregation can be reversed by an appropriate treatment. In forced aging, the azo dyes react in two steps: a partial and reversible deaggregation followed by a much slower, irreversible oxidation. The Arrhenius method for extrapolation of stability data to lower temperatures is therefore probably not applicable to Cibachrome materials. See also AATA 21-11. -- AATA