Vegetable, chrome, semichrome, and chrome retan leathers were adjusted to various pH values in the range 2 to 9 and stored at 40° C. over water for 15 weeks. The strength of the leathers as measured by buckle tear load was little affected by the adjustment of pH except when this was reduced below 3.0. In general, in the range 4 to 8 pH had little effect on the losses of strength of chrome, vegetable and semichrome leathers, but with the retan leather losses increased progressively with fall in pH. In this range the chrome leather lost no strength, the vegetable-tanned leather about 30per thousand, the semichrome about 50per thousand, and the chrome retan leather about 10per thousand at pH 8.0, increasing to 25per thousand at pH 4.0. At lower pH values the losses in strength of the chrome and retan leathers increased sharply but those of the semichrome only slightly, while with the vegetable-tanned leather, losses were only increased at the lowest pH value (2.0). At this pH, however, the vegetable-tanned leather was extensively damaged after only two weeks' storage. The leathers containing vegetable tan became progressively darker in color with increasing pH and tended to become cracky, but the chrome-tanned leather was relatively unaffected both in appearance and feel. It is concluded that for resistance to storage the pH of the leather should be above 3.5, and even higher with chrome leather and retan leather. High pH values, however, lead to darkening of leathers containing vegetable tannins and to detannage of chrome leather, so that a limit must be set. In wear, the absorption of perspiration increases the pH of the leather, and this must also be borne mind.