To obtain long-term atmospheric corrosion data for weathering steels such as ASTM A 242 Type 1 (USS COR-TEN A) and ASTM A 588 Gr. A (USS COR-TEN B), an exposure program was initiated in which test panels were exposed for up to sixteen years at three corrosion test sites in the eastern United States. A unique feature of this program was that test panels were exposed in four different orientations (30°S, 30°N, 90°S, 90°N) at each site. The results confirmed the superior resistance of the weathering steels as compared to that of copper-bearing steel and carbon steel under virtually all the test conditions, with the A 242 steel being the most corrosion resistant. Overall, the rural test site (Potter County, PA), which is in line with the prevailing winds carrying acid-rain constituents from the middle western United States, was about twice as corrosive to these steels as was the urban-industrial site (Kearny, NJ), whereas the moderate-marine site (Kure Beach, NC, 250 m) was about ten times as corrosive as was the urban-industrial site. With respect to the effect of test panel orientation, the south-facing panels tended to show lower corrosion rates than did the north-facing panels at all the test sites. Also, in most cases, the inclined (30°) panels showed lower rates than did the vertical (90°) panels.