With 0.4 g l(-1) arachidonic acid (AA) added to the medium after 36 h fermentation, beta-carotene production in mated cultures of Blakeslea trispora was 73 % higher than that of the control at 690 mg l(-1). With the treatment of AA, the transcriptional levels of genes hmgR, carRA and carB, that are involved in carotene biosynthesis, increased by 31, 22 and 39 %, respectively.