OBJECTIVE: To compare indicators of systemic inflammatory response in the second trimester in women who developed pre-eclampsia with normal pregnancies. DESIGN: Prospective nested case control study derived from a cohort of 2190 pregnant women. Blood samples were obtained at 18 weeks of gestation. The following inflammatory parameters were measured: tumour necrosis factor-alpha (TNF-alpha), plasminogen activator inhibitor-1 (PAI-1), interleukin-1beta (IL-1beta), IL-6, IL-10, microCRP and tissue factor (TF). SETTING: Institute of Medical Genetics, University of Oslo, and Department of Medical Genetics, Ullevål University Hospital and Departments of Obstetrics and Gynecology, Aker University Hospital, Oslo, Norway. SAMPLE: The cases were 71 women who subsequently developed pre-eclampsia. The controls were 71 healthy, pregnant women matched for age, parity and first trimester body mass index (BMI). METHODS: Venous blood was drawn from fasting subjects into 5 mL test tubes containing EDTA. Samples were analysed for inflammatory parameters: IL-1-beta, IL-6, IL-10, TNF-alpha, PAI-1, TF (ELISA-technique) and CRP (latex-enhanced immunonephelometric assay), strictly according to the manufacturer's recommendation. MAIN OUTCOME MEASURES: The matched case and control subjects were compared by the paired two-tailed Wilcoxon signed rank test. All P values were two-tailed and P