Pre-eclampsia (PE) is associated with increased oxidative stress and excessive maternal inflammatory response. Heme oxygenase 1 (HMOX1) is an important stress response enzyme and a mediator of cytoprotection against a wide variety of tissue injuries. In the present study, microarray technology was used to compare the expression of HMOX1 and other genes involved in stress and inflammatory responses in decidua basalis from 16 pregnancies complicated by PE and 17 healthy controls. In addition, the presence of HMOX1 protein in decidua basalis was examined by means of immunohistochemistry, and ELISA was used to measure the maternal serum concentration of HMOX1. Fifteen transcripts involved in stress response including HMOX1 were up-regulated in cases, using a cut-off value at p=0.01. HMOX1 protein expression in decidua basalis was significantly increased in cases compared to controls reflected by more pronounced intensity of HMOX1 positive decidual cells (1.8±0.3 versus 1.5±0.4, p=0.02) and an increased proportion of HMOX1 positive decidual leukocytes (31±29 versus 9±6%, p=0.001). Finally, serum HMOX1 levels were significantly higher among cases compared to controls (3.1±1.3 versus 1.9±0.5 ng/ml, p=0.008). Increased decidual and serum HMOX1 levels, together with altered decidual expression of some stress-related genes in cases, support the role of oxidative stress and excessive maternal inflammatory response in the pathogenesis of PE.