Two series of reinforced concrete beams were made and exposed to severe natural weathering at Treat Island, Maine. Variables under study were thickness of concrete cover over and tensile stress in the reinforcing steel, position of the steel, and type of concrete and steel used. Results after 15 winters of exposure of the first series of beams (Series A) indicated that the air-entrained beams were significantly more resistant to the weathering that the nonair-entrained beams, and that the beams with reinforcing steel having deformations conforming to ASTM Standard A 305 were more resistant to the weathering than those with reinforcing steel having old-style deformations. Results after 12 winters of exposure of the second series of beams (Series B) indicated that more exposure is needed to produce deterioration sufficient to permit unambiguous conclusions.