The outdoor corrosion resistance of bare steel and zinc-electroplated steel (15 μm thickness) was studied over a period of four years at 11 outdoor exposure sites in the metropolitan area of Barcelona. The results obtained were evaluated by means of the mass loss method and by the ASTM 'rating number' method. The corrosion observed in the exposed samples (uncoated steel and zinc electroplated steel) is discussed, as well as the influence of relative humidity, chlorides, sulphur dioxide and particles in suspension. Bare steel specimens were much more corroded than zinc-electroplated steel specimens. The corrosion increased in marine environment for both types of specimens. © 1993.