Polyacrylonitrile (PAN) membranes for ultra- and microfiltration were developed by GKSS. They are fabricated on a non-woven by a phase inversion process. It is shown that the formation process mainly depends on the polymer concentration of the casting solution as well as on the temperature of the precipitation bath. Therefore, different membrane morphologies can be obtained. They vary from large finger-like pores to homogeneous microporous structures. The flux of the membranes can be adjusted between 100 up to nearly 2000 l/m(2) h bar with high rejection. PAN membranes have good chemical stabilities and can be welded by heat or ultrasound. This makes the production of membrane envelopes possible, which are used in several filtration module types like Amafilter PM and Rochem FM. Today the membranes are commercially available and used in several applications such as water treatment, concentration of whey or protein, concentration of oil/water mixtures, etc. In these applications the membrane demonstrated high stability against chemical cleaning agents. It resists sodium hypochlorite, citric acid and weak alkaline solutions.