Introduction: Preeclampsia is a pregnancy-specific syndrome that occurs after the 20 weeks of pregnancy, and is characterized by hypertension and proteinuria. It complicates approximately 5-6% of all pregnancies and is a major factor in fetal and neonatal mortality. Objectives: The aim of this study was to evaluate serum concentration of soluble endoglin (sEng) as the predictorn of preeclampsia in pregnant women with hypertension. Material and methods: The study was conducted at the Department of Pathology of Pregnancy (Department of Gynecology and Obstetrics, Medical University of Lodz), and the clinical ambulatory of the WSSz – M. Madurowicz (at present, WSSz – M. Pirogow) in Lodz, between 2008-2012. The Committee of Bioethics, Medical University of Lodz approved of the research (RNN/106/08/KE, May 20, 2008). The study included 86 pregnant women, between 25 and 40 weeks of pregnancy. The subjects were divided into 3 groups: – Group HA – 33 pregnant women with hypertension arterialis (≥140/90 mmHg) without proteinuria, – Group P – 21 pregnant women with hypertension arterialis (≥140/90 mmHg) with proteinuria, – Group K – 32 pregnant women with normal blood pressure (<140/90 mmHg) without proteinuria. Markings were determined with the ELISA method, using Quantikine kit. Results: A significantly higher value of endoglin levels were found in pregnant women with preeclampsia syndrome (P) than in women with hypertension (HA) and the control group (K). Levels of endoglin in the P group was 29.70 pg/ml, 19.54 pg/ml in the HA group and 12.99 pg/ml in the K group. Conclusions: Elevated serum concentration of soluble endoglin (SENG) in pregnant women constitutes a risk factor for preeclampsia.