Yarrowia lipolytica, grown in a nitrogen-limited continuous culture (D = 0.032 h(-1)), produced 9.3 g dry biomass l(-1), which contained 0.25 g oil g(-1). When an aqueous extract from Teucrium polium L. was added, the biomass concentration remained constant while the oil content increased to 0.33 g oil g(-1) dry weight. The specific rate of oil formation increased from 7.9 to 10.6 mg oil g(-1) biomass h.