The stability of chlorine-containing fungicides was studied by observing the amounts of Clup>-released in a benzene-HNOub>3 mixture at 80 degrees C. The stability under these conditions was presumed to give an indication of their stability in leather. Among nine fungicides studied, the amount of Clup>-released ranged from 0 to 13% of the total chlorine content. Eight of the compounds were chlorophenols. The liberation of Clup>-from chlorophenols appears to be facilitated by electronic effects that increase the electron density on the carbon to which chlorine is attached. The effects of various fungicide treatments on leather deterioration under accelerated aging conditions were also investigated. Organically bound copper, chlorine, or chloride ions are less harmful to leather than copper or iron ions. There are some indications, however, that fungicides containing organically bound copper or chlorine may not be completely harmless.