Objective Evaluation of morphology and secondary metabolites production inAspergillus terreusATCC 20542 cultures over a wide range of lactose and yeast extract concentrations from 0.2 up to an extremely high level of 200 g l(-l). Results The morphological differences of mycelial objects were quantified with the use of morphological parameters calculated by applying the tools of digital image analysis. At 200 g l(-l)of yeast extract clumps and loose hyphae were recorded instead of pellets commonly observed in submerged cultures ofA. terreus. Under these conditions the biosynthesis of (+)-geodin and asterric acid was totally blocked, lovastatin formation was found to be at a relatively low level and biomass production turned out to be greater than in the remaining variants, where the pelleted growth was observed. At 200 g l(-l)of lactose the production of lovastatin, (+)-geodin and asterric acid was visibly stimulated compared to the media containing 0.2, 2 and 20 g l(-l)of the sugar substrate, but at the same time no traces of butyrolactone I could be detected in the broth. Lactose at the extremely high concentration of 200 g l(-l)did not induce the drastic morphological changes observed in the case of 200 g l(-1)of yeast extract. It was proved that at the C/N values as low as 4 and as high as 374A. terreusnot only continued to display growth but also exhibited the production of secondary metabolites. The use of cultivation media representing the equivalent C/N ratios led to different metabolic and morphological outcomes depending on the concentration of lactose and yeast extract that contributed to the given C/N value. Conclusion The extremely high concentration of yeast extract leads to marked morphological changes ofA. terreusand the elimination of (+)-geodin and asterric production, while applying the excess of lactose is stimulatory in terms of lovastatin production.