OBJECTIVE: To evaluate the role of CD68(+) macrophages and inflammatory/signaling proteins in the decidua of singleton pregnancies with late-onset pre-eclampsia. PATIENTS AND METHODS: This study was designed as a prospective case-control study. Decidual tissue samples were obtained from twenty healthy pregnant women as a control group and twenty pregnant women with late-onset pre-eclampsia showing severe symptoms as the study group. We examined the abundance of CD68(+) macrophages in both groups using flow cytometry. Protein and mRNA expression levels of inflammatory/signaling proteins, including inducible nitric oxide synthase. nuclear factor-kappa B inhibitor alpha, cyclooxygenase-2, and phosphorylated c-Jun N-terminal kinase, in the decidua of both groups were measured using Western blotting and Reverse Transcription-Polymerase Chain Reaction. respectively. Student's t-tests were performed for statistical analysis. RESULTS: The numbers of CD68(+) macrophages were similar in the study and control groups (p=0.47). However, the levels of inducible nitric oxide synthase, nuclear factor-kappa B, cyclooxygenase-2, and phosphorylated c-Jun N-terminal kinase were significantly increased in the study group. Therefore. pro-inflammatory mediators and signaling proteins in the decidua during pre-eclampsia may be related to the pathogenesis of pre-eclampsia. CONCLUSIONS: Pre-eclampsia-induced alterations in the expression of inflammatory/signaling proteins in the decidua during singleton pregnancies may play a critical role in the pathogenesis of pre-eclampsia.