The adaptive response of the fungus Blakeslea trispora to the oxidative stress induced by iron ions during carotene production in shake flask culture was investigated. The culture response to oxidative stress was studied by measuring the specific activities of catalase (CAT) and superoxide dismutase (SOD). The addition of 1.0 mM of FeCl3 to the medium was associated with a mild oxidative stress as evidenced by remarkable increase of the specific activities of SOD and CAT. On the other hand, the addition 5.0 mM of FeCl3 caused a strong oxidative stress resulting in a drastic decrease in carotene concentration. The oxidative stress in B. trispora changed the composition of the carotenes and caused a significant increase of gamma-carotene ratio. The highest concentration of carotenes (115.0 +/- 3.5 mg/g dry biomass) was obtained in the basal medium without the addition of FeCl3 after 8 days of fermentation. In this case, the carotenes consisted of beta-carotene (46.3 %), gamma-carotene (40.1 %), and lycopene (13.6 %). The addition of 1.0 mM of FeCl3 into the medium did not change the concentration of carotenes. But, the composition of carotenes was changed with a drastic increase of gamma-carotene ratio (61.6 %) and a decrease in beta-carotene and lycopene ratio (31.2 and 7.2 %, respectively).