Until recently, in desalination plants seawater was pre-treated with a combination of conventional techniques such as air flotation, clarification, sand filtration and cartridge filtration prior to spiral wound reverse osmosis desalination membranes. Microfiltration or ultrafiltration membranes are now considered as an alternative solution for seawater pre-treatment. This paper describes pilot test results obtained at three different locations treating Mediterranean seawater using 0.1 mum hollow fiber membranes in Pall's Microza modules. Depending of the location, the pilots operated with or without pretreatment using ferric chloride and with or without specific flux maintenance (SFM) protocols performing daily highly chlorinated backwash. The study shows that system optimization yields stable, reproducible permeate flow and permeate SDI of 1.8 or less, with mean SDI of 1.43 when seawater was coagulated or SFM was performed. At these conditions, reverse osmosis system recovery is enhanced and total integrated system performance is optimized.