In this work the effect of several organic nitrogen sources on lipase production in Yarrowia lipolytica LgX64.81 overproducing mutant was studied. Among them, tryptone and peptone showed the most prominent stimulatory effect. Interestingly, only tryptic and peptic casein digest were found to highly induce lipase biosynthesis while lipase production was very limited in the presence of casein digest from papain and pronase-catalysed hydrolysis and absent in case of chymotryptic digest. It was also demonstrated that the stimulatory peptides should be present in the culture medium at specific proportions and molecular size to match the physiological requirement of Yarrowia lipolytica strain for lipase biosynthesis. Herein, the lipase-production stimulatory peptides were isolated by ion exchange chromatography for the first time. These results had contributed to gain an insight on tryptone role in lipase production by Yarrowia lipolytica. Moreover the use of a chemically defined medium supplemented with the isolated peptides, will improve the efficiency of the process for lipase production in this yeast. (C) 2008 Elsevier Ltd. All rights reserved