The filamentous fungus Aspergillus fumigatus is an opportunistic pathogen which causes life-threatening diseases in immunocompromised patients. Resistance of A. fumigatus against azole class compounds continues to pose a threat to human health worldwide. How this fungus maintains fitness before any resistance causing mutations arise is not well understood. In this study, we use RNA-seq to demonstrate how A. fumigatus exerts its phenotypic plasticity when exposed to itraconazole, and which important cellular processes contribute to its adaptation to a new, stressful environment containing azole compounds. We conducted an in vitro assay in which we exposed 24h old mycelia of clinical A. fumigatus isolates grown at 37°C, to sublethal concentrations of itraconazole which might permit gradual adaptation of the fungus to the new, stressful environment. Mycelia were then harvested after 30, 60, 120 or 240 minutes respectively, and relative expression was compared to the mycelia harvested directly after 24h without the addition of itraconazole.