The extent of corrosion of metal objects on board the WASA (which sank in Stockholm harbor in 1628) is discussed. In particular, iron cannonballs, lead bullets and copper irons were examined as the original weights and dimensions of these were known. The average extent of corrosion of the iron over 333 years was 40-50% (average rust layer 14 mm) although the caliber of the balls remained the same. The corrosion depth for the lead bullets was 0.85 mm and the corrosion loss of the copper irons was 880-3640 g/m² depending on the position of the coins in the ship. Experiments carried out over a period of flve years under simulated conditions agree well with these figures. The cannon balls were treated in a hydrogen reduction fumace at 600° C and the lead bullets in a 10% ammonium acetate solution for half an hour followed by brushing and drying. -- AATA