Mortierella alpina LPM 301, a producer of arachidonic acid (ARA), was found to possess a unique property of intense lipid synthesis in the period of active mycelium growth. Under batch cultivation of this strain in glucose-containing media with potassium nitrate or urea, the bulk of lipids (28-35% of dry biomass) was produced at the end of the exponential growth phase and remained almost unaltered in the stationary phase. The ARA content of lipids comprised 42-50% at the beginning of the stationary phase and increased continuously after glucose depletion in the medium due to the turnover of intracellular fatty acids; by the end of fermentation (189-210 h), the amount of ARA reached 46-60% of the total fatty acids (16-19% of dry mycelium). Plausible regulatory mechanisms of the growth-coupled lipid synthesis in microorganisms are discussed.