Kinetic analysis of arachidonic acid (AA)-oil biosynthesis by Mortierella alpina 1S-4 growing under lipid-accumulating (LN medium) and non-lipid-accumulating (HN medium) conditions was investigated and compared with industrial AA fermentation. Various kinetic parameters of these cultivation processes demonstrate a characteristic pattern of the lipogenesis in this fungus, where growth phase, phase of oil accumulation and phase of AA synthesis are distinct from each other. The fungus utilizing LN medium synthesized 32.3 g fatty. acid 100 g(-1) glucose on the 4th day of cultivation and reached the maximum daily fatty acid accumulation (expressed as differential specific rate q(D(FA/B))) Of 9.5%. Our results also indicate that a qD(FA/B) value of about 2.5% might be critical for lipid overproduction in M. alpina. AA was rapidly incorporated into triacylglycerols (90% of total AA) at the later cultivation phase and overall AA yield was directly related to the total yield of fatty acid.