Pseudomonas aeruginosa bacteria was sepd. from the rhamnolipid-contg. fermentation broth by ultrafiltration through a com. polysulfone membrane (cut-off 100 kDa) under cross-flow mode conditions (up to 2 bar). At the bacteria concn. 2 g/L, the flux of the suspension 100 L/m(2)h was achieved.