The properties of wool after treatment with sodium hydroxide in a series of 2 M aqueous salt solutions show that anions protect from alkaline degradation in the order S2O3 z, SO8 z, citrate > CO3 z> 504 z > C2H 3O2- > Cl- > Br- > NO2- > I- > CNS-, while cations protect in the order Li+, Na+ > K+. The swelling of wool is decreased by some 2 M salt solutions (S2O2 z) but is unaffected by others (CNS-). However, the rate of sorption of OH- by wool is the same from all the alkaline 2 M salt solutions and from pure NaOH. The anion concentration in solution either increases (S2O2 z) when wool is added, or is unaffected (2 M CNS-); that is, water is sorbed preferentially from some salt solutions, but no specific anion sorption occurs. Salt effects on wool are therefore unlikely to be due to dehydration of the wool or to ion binding. The present results, and many other protein properties, can be simply explained on the basis of the effective pressure exerted by salts in solution, a concept introduced by Gibson [8]. Results of practical interest are that wool can be shrinkproofed without damage by treatment with certain aqueous sodium hydroxide solutions and that yellowing of wool in alkali can be prevented by the addition of reducing agents, such as sodium bisulfite, to the solution.