Coatings of polyethylene, polyvinylchloride, and evaporated A1 were tested for their effectiveness in suppressing fatigue damage in pure aluminum and 7075-T6 alloy. On pure aluminum, a polymer coating suppresses Stage I fatigue cracking if the coating is applied to a surface possessing a dehydrated oxide. On 7075-T6 alloy, a polymer coating has no effect. These results are discussed in terms of the water vapor effect on the elastic modulus of aluminum oxide and the resulting influence on near-surface dislocations. Author, modified-PL.