In 1932, specimens of all commercially available structural aluminum alloys as well as some experimental alloys were exposed for long-time weather exposure tests at Coco Solo, Canal Zone, Norfolk, Va., and Washington, D. C. The order of merit with regard to corrosion resistance of these alloys was the same for all localities, although the urban atmosphere at Washington was considerably less corrosive than either of the marine atmospheres. Examination after approximately 20 years of exposure revealed that all of the non-heat-treatable alloys containing less than 4 per cent of magnesium and one containing about 1 per cent of manganese were very resistant to corrosion. Of the heat-treatable alloys, the clad varieties and one alloyed with about 2 per cent of cadmium were quite corrosion resistant, while those containing copper, silicon, and manganese were the least resistant. Aluminum-copper alloys were very susceptible to intergranular corrosion and rapid disintegration when improperly quenched or artificially aged unless they were adequately protected. Anodically formed surface films increased the corrosion resistance of the alloys more than did the films formed by immersion in chemical solutions. The most protective paints were those pigmented with zinc chromate and, to a lesser extent, those with aluminum powder. Almost complete protection was afforded by anodically-formed surface films coated with paints pigmented with zinc chromate or aluminum powder or both.