Particle swarm optimization was used to improve the medium for the production of Echinocandin B (ECB) by Aspergillus nidulans. Fifteen medium ingredients were optimized using a total of 135 shake-flask fermentations (nine iterations). The best medium improved titre by 41%. A traditional statistical design approach using similar numbers of shake-flask fermentations improved the titre by 46%. by optimizing five ingredients screened from the original 15. The PSO approach yielded a different optimum medium than the statistical design methods used. (C) 2001 Elsevier Science Ltd. All rights reserved.