The importance of membrane technologies for waste water treatment has increased in recent years. In contrast to conventional organic membranes, inorganic membranes have a high mechanical, chemical and thermal persistence. They may be regenerated and there is no ageing process of the membrane material. To ascertain the advantages and disadvantages of various types of membranes agricultural waste waters such as wash water of potatoes and carrots, pig and cattle slurry and waste water of milking plants were tested. The studies were carried out under constant conditions for pressure, temperature and GOD-concentration in the feed. The main results are: Compared with organic membranes PS-50,000 (cut-off: 50,000 g/mole) and PES-40,000 (cut-off: 40,000 g/mole), the inorganic membrane SiC-0.05 (cut-off: 0.05 mu m) had the greatest permeate flux and the best GOD-rejection for cattle slurry, waste water of milking plants, wash water of potatoes and pig slurry. Compared with the membrane SiC-0.2 (cut-off: 0.2 mu m) the membrane SiC-0.05 had a greater permeate flux and COD-rejection. The optimum transmembrane pressure amounts to 2 bar for the membrane SiC-0.05. A higher pressure does not lead to a proportional increase of the permeate flux. There is no significant difference in permeate flux and COD-rejection (ultrafiltration of wash water of potatoes and carrots) between inorganic membranes Al2O3-0.1 (cut-off: 0.1 mu m) and SiC-0.05, although the membrane cut-off for Al2O3-0.1 is much lower.