High rhamnolipid productivity (32 g/l) was obtained in an ethanol fed-batch culture of Pseudomonas aeruginosa IFO 3924. Examination of the autoinducer level and exogeneous autoinducer addition tests indicated that in the fed-batch system high autoinducer activity, which was about ten-fold that obtained In an unfed system, was thought to be the cause of the high rate of rhamnolipid production. Both N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) and N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL) enhanced rhamnolipid productivity in the unfed system.