Strain-cycle fatigue data were obtained in both ambient air and substitute ocean water for sheet grades AISI 1012, Galvalume, galvanized B50XK and B80RK, and BethStar 80 plate. The results show that the cyclic stress-strain curves are identical for ambient air and substitute ocean water. For the life range beyond 105 reversals, ambient air fatigue resistance is proportional to tensile strength. In substitute ocean water, the strain for a given life is less than for ambient air and is virtually independent of strength level. Galvalume and galvanized coatings have a beneficial effect on life in substitute ocean water at high strain amplitude and low cyclic frequency. For tests at low strain amplitude and low frequency, coated and bare steels have about the same fatigue resistance in substitute ocean water.