A local isolate of Aspergillus terreus was selected among different microorganisms as a new cyclosporin A (Cy A) producing culture. The formation of Cy A was investigated under different fermentation conditions (including selection of the cultivation medium, fermentation time course, inoculum nature, medium volume, agitation rate, pH value). Relatively high Cy A productivities were maintained when the fermentation process was carried out using a medium composed of (g/L): glucose, 50; bactopeptone, 10; KH(2)PO(4), 5; KCl, 2.5; pH 5.3, inoculated with 2% standard inoculum of 48 h age, shaken at 200 rpm for 10 days.