In an attempt to find an on-line method to remove oxide deposited during normal operation on the primary side of a steam generator, a series of experiments was undertaken in a high temperature recirculating autoclave system. Alloy-600 steam generator tubes removed from a CANDU nuclear reactor were monitored on-line with a gamma spectrometer and the effects on them of transients in pH, oxidizing condition of the coolant and temperature, alone and in combination, were attempted. Only a chemical process-the addition of a mixture of ethylenediaminetetraacetic acid (EDTA) and citric acid-was effective in removing radioactivity and, therefore, oxide.