The aim of this study was the evaluation of serum procalcitonin (PCT) concentrations in pregnancy complicated by premature rupture of membranes (PROM) before 36 weeks of gestation. The study group consisted of 42 women with PROM between 25. and 35. week of pregnancy. The control group comprised 38 patients between 24.-35. weeks of pregnancy in acute phase of imminent preterm labor with intact membranes. All of them, after successful treatment in the hospital, delivered near term. In both groups serum PCT concentrations were higher than in healthy patients without pregnancy as compared to literature data. It was also stated that in women with PROM before 36. week of gestation serum PCT concentrations are significantly higher than in pregnant women in acute phase of imminent preterm labor with intact membranes who after successful treatment deliver near term.