Laboratory corrosion studies of the steam generator tubing materials Inconel Alloy 600, Incoloy 800, and Monel 400 have been performed. Tests were carried out at 288ºC on tubing sections that were internally heated to provide heat transfer through the tube wall. In exposures to lakewater, pitting attack was apparent in crevice regions and under deposits. A crystallographic pitting morphology was usually found on Alloy 600 and Incoloy 800 and was likely caused by acid chloride attack. Attack on Monel 400, however, was mainly intergranular in nature. In tests performed on Alloy 600 in solutions of specific anions, attack was found to occur in silicate solutions in the presence of magnetite sludge. Although these tests were performed in solutions more concentrated than those likely to be found in operating steam generators, they do suggest that strict adherence to secondary water chemistry specifications is required to protect against the possibility of pitting corrosion. In comparing the performance of three alloys tested, Incoloy 800 appears to exhibit greater resistance to pitting corrosion than Alloy 600 or Monel 400 in lakewater environments