Degradation-promoting action of a series of ferrous and titanium alloys on CF3O(CF2O)(x)(CF2CF2O)(y)CF3-based Z25 fluids and the inhibition effectiveness of several classes of additives were investigated. Four types of additives-phosphines, phosphates, phospha-s-triazines, and diphosphatetraazacyclooctatetraene-were studied in two batches of 225 fluid, P28 and P151. In the absence of inhibitors, titanium alloys were more detrimental than the ferrous metals, but the additives were more effective in the presence of titanium alloys. Phosphate esters totally inhibited the decomposition of P151 at 330 degrees C over 24 h in both types of alloys. The other additives were effective at lower temperatures. The responsiveness of fluid to an additive was found to be batch dependent.