There is little knowledge of the effect of acclimatization of Aspergillus flavus strains to climate-related abiotic factors and the subsequent effects on growth and aflatoxin B-1 (AFB(1)) production. In this study, two strains of A. flavus (AB3, AB10) were acclimatized for five generations in elevated CO2 (1000 ppm x 37 degrees C) on a milled pistachio-based medium. A comparison was made of the effects of non-acclimatized strains and those that were acclimatized when colonizing layers of pistachio nuts exposed to 35 or 37 degrees C, 400 or 1000 ppm CO2, and 0.93 or 0.98 water activity (a(w)), respectively. Acclimatization influenced the fitness in terms of the growth of one strain, while there was no significant effect on the other strain when colonizing pistachio nuts. AFB(1), production was significantly stimulated after ten days colonization when comparing the non-acclimatized and the acclimatized AB3 strain. However, there was no significant increase when comparing these for strain AB10. This suggests that there may be inter-strain differences in the effects of acclimatization and this could have a differential influence on the mycotoxin contamination of such commodities.