Isoamyl acetate is a natural flavour ester, widely used as a source of banana flavour by the food industry. Williopsis saturnus var. saturnus is a yeast which can produce isoamyl acetate by esterification of amyl alcohols with acetyl coenzyme A via fermentation. The evaluation of this kind of production as an alternative way to obtain natural banana flavour could be possible, if the levels produced were high enough to make a commercial product. In this study, the effects of temperature (15 degrees C and 25 degrees C) and aeration (aerobic, semiaerobic, and anaerobic) on the production of isoamyl acetate by Williopsis saturnus var. saturnus from sugar beet molasses were examined. According to the results obtained, isoamyl acetate production rate and specific productivity were higher at 25 degrees C than at 15 degrees C and at semiaerobic condition than aerobic and anaerobic conditions. Williopsis saturnus var. saturnus showed a production rate of 0.703 mg L-1 h(-1) and a specific productivity of 0.0297 mg L-1 cell(-1) h(-1) isoamyl acetate with semiaerobic condition at 25 degrees C. The maximum amount of isoamyl acetate reached with these conditions was 118 mg/L.