Objective. To evaluate differences in plasma cytokine levels longitudinally in pre-eclamptic and normotensive pregnancies. An increased inflammatory response has long been associated with pre-eclampsia, both early and late in the pre-eclamptic pregnancy. Design. Blood samples were collected longitudinally during pregnancy from a cohort of 1 631 pregnant women. Thirty-two women with pre-eclampsia and 67 normotensive pregnant women were identified from the cohort. Setting. A Danish regional hospital. Samples. Samples were collected from the 18th week of pregnancy until delivery and divided into the following four gestational intervals: <25th week, 26th–29th week, 30th–35th week and >36th week. Methods. Simultaneous measurement of all nine cytokines was done using a capture bead system. Main Outcome Measures. Plasma levels of interleukin (IL)-1β, IL-2, IL-4, IL-6, IL-8, IL-10, tumor necrosis factor-α, interferon-γ and granulocyte macrophage colony-stimulating factor during pre-eclamptic and normotensive pregnancies. Results. Pre-eclampsia was associated with increased tumor necrosis factor-α between the 26th and 29th week (p=0.0421) and increased IL-6 after the 36th week (p=0.0044). The other cytokines measured were comparable in the two groups. Conclusions. This large prospective collection of blood samples was undertaken to determine inflammatory status during pre-eclamptic and normotensive pregnancies. Our results support a tendency towards increased inflammation in pre-eclampsia, but the measured cytokines are not eligible for prediction, monitoring or diagnosing pre-eclampsia.