This paper summarizes a study that aimed to estimate maternal and umbilical serum angiotensin-converting enzyme (ACE) activity in singleton pregnancies complicated by preeclampsia. This study was carried out at the University Medical School of Lublin in Poland on 17 patients with singleton pregnancy complicated by preeclampsia between 33 and 40 weeks of gestation. Meanwhile the control group consisted of 14 healthy normotensive patients with singleton uncomplicated pregnancy and normal laboratory tests. The serum ACE activity was estimated using spectrophotometry. It was noted that there were no statistically significant differences in patients profiles between groups in gravidity parity maternal age gestational age and the mode of delivery. Overall the study revealed elevated maternal and umbilical serum ACE activity in pregnancies complicated by preeclampsia. Hence it indicates a significant role of ACE in pregnancy complicated by preeclampsia.