Objective: To compare concentrations of interleukin-10 in patients with preeclampsia and healthy normotensive pregnant women. Material and methods One hundred patients were selected. Fifty preeclamptic patients were selected as cases (group A) and 50 healthy pregnant women with a similar age and body mass index to those in the study group were selected as controls (group B). Blood samples for interleukin-10 determination were collected in all patients before labor and immediately after diagnosis in the study group. Results: There were no significant differences in maternal or gestational age or body mass index at sample collection (p=ns). Significant differences were found between groups in mean values of systolic and diastolic blood pressure (p<0.05). Statistically significant differences were also found in interleukin-10 concentrations in patients in group A (15.9 +/- 3.1 pg/ml) and patients in group B (90.6 +/- 20.0 pg/ml p<0.05) and a strong, negative and significant correlation was found with systolic (r=-0.823; p<0.05) and diastolic blood pressure (r=-0.825; p<0.05). Conclusion: Interleukin-10 concentrations of were significantly lower in preeclamptic patients than in healthy normotensive pregnant women. (C) 2009 Elsevier Espana, S.L. All rights reserved.