Ammonium bisulfide has been the well known main culprit of aqueous corrosion in hydroprocessing units. A lesser understood and, at times, more menacing aqueous corrosion problem in these units has been due to chloride salts. Chlorides can be introduced into the system through the feed and/or through the make-up hydrogen gas. This paper describes case histories of chloride related problems and the means for minimizing such occurrences.