Aspergillus fumigatus causes lethal invasive aspergillosis in cortisone-treated mice while immunized mice are protected. Kinetics of interferon (IFN)-gamma, tumor necrosis factor-alpha, interleukin (IL)-12p40, IL-4 and IL-10 expression were assessed by reverse transcription-PCR in the spleen and lungs of mice. After immunization, mice were protected from otherwise lethal infection, with concomitant high expression levels of IFN-gamma early in the lungs and later in the spleen. In the lethal infection model cortisone-treated infected mice presented high expression levels of IL-10 in the spleen and in the lungs. Immunocompetent mice were able to control the disease and presented earlier expression of IL-12p40 and IFN-gamma in lungs and spleen. These results confirm the importance of Th1 dependent immunity against invasive aspergillosis.