The corrosion resistance of Type 316 stainless steel, partly embedded in concrete, partly exposed to stagnant seawater and partly exposed to flowing seawater, has been determined over various periods up to about 12 one-half years duration. The exposure tests were carried out in full immersion and tidal conditions, on specially designed concrete blocks. Mild steel specimens were also tested for comparison. Ordinary Portland cement concrete gave more protection to the stainless steel than did sulphate-resisting Portland cement concrete.