New products based on enhanced maleate chemistry have been developed to control the broad range of deposits found in thermal desalination plants. To investigate the performance characteristics of enhanced maleate products, laboratory tests were developed to measure the control of fouling species. The test methods developed for and used in this study provide a further understanding of the key mechanisms of deposit control by additives. The advance performance of products based on enhanced maleate chemistry, compared with conventional products currently in use in MSF and MED plants will be presented. Individual product data sets have been combined to produce product performance profiles which can then be used in the selection of additive appropriate to the fouling characteristics of the desalination plant. The enhanced maleates have been successfully tried in both MSF and MED plants. Six months＇ data from a 23,000 m(3)/d plant in Saudi Arabia, operated at a top brine temperature of 110 degrees C, will be presented. Also 12-month operational data from an 8000 m(3)/d MED plant in Europe, top brine temperature 62 degrees C, will be presented. The results from these extended field evaluations have confirmed the initial laboratory results.