The successful development of geothermal reservoirs to generate electric power will require the injection disposal of approximately 700,000 gal/h (2.0 x 106 l/h) of heat-depleted brine for every 50,000 kW of generating capacity. To maintain injectability, the spent brine must be compatible with the receiving formation. The factors that influence this brine/formation compatibility and tests to quantify them are discussed in this report