Pulmonary aspergillosis which is an important opportunistic infection in neutropenic patients, is usually caused by Aspergillus fumigatus. Since the pathogenesis of disease is not well understood, the main proposed mechanism is thought to be cell-mediated immunity and cytokine response. The aim of this study was to investigate the local production of cytokines in the lung tissues of rats with experimentally developed aspergillosis, by reverse transcriptase-polymerase chain reaction (RT-PCR). A total of 33 Wistar albino type rats were included in the study with the consent of Experimental Animal Ethics Committee. Twenty-five of the rats were infected with A.fumigatus by intratracheal way, while 8 animals were used as controls. The presence of A.fumigatus in the lung tissues of infected rats was confirmed with the use of quantitative culture and histologic staining methods. RNA isolation from the lung tissue samples of both groups were performed by a commercial kit (Qiagen, Germany). After obtaining complementary DNAs from the genomic RNAs, in-house qualitative and quantitative (real-time) PCR methods were used to amplify the target regions for interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) by using specific primers (Tib Molbiol, Germany). Mean mRNA levels achieved by real-time PCR for IL-10, TNF-alpha and IFN-gamma in aspergillosis group were 6.5 x 10(6) copies/ml, 7.9 x 10(5) copies/ml and 2.2 x 10(3) copies/ml, respectively, while those values in control group were 4.3 x 10(2) copies/ml, 5.6 x 10(3) copies/ml and 1.3 x 10(2) copies/ml, respectively. Our data indicated that rat model of aspergillosis was associated with significantly increased expression of mRNA encoding IL-10 and TNF-alpha than controls (p< 0.05), however there was no statistically significant difference between the groups with respect to IFN-gamma expression (p= 0.53). In conclusion, the production of proinflammatory cytokines which mediate the influx of phagocytic cells might account for the localization of Aspergillus infection to the upper respiratory tract. The up-regulation of the expression of the immunomodulatory cytokine TNF-alpha and IL-10 in lung tissue from infected rats might be important to limit the extent of local tissue destruction, but might also account for the fact that infected rats are generally unable to clear the infection spontaneously.