The preterm birth (PTB) is still a problem for the modern obstetrics, with certainly unsolved questions. Mainly this is associated with the lack of chance to decrease its frequency but also due to the tendency of definite change of its structure--high level of extreme premature state. Intra uterus infection (IUI) is one of the major etiologic reasons for PTB. The early detection of IUI and the determination of the level of fetus damage are the leading therapeutic approach to PTB. The present study includes the test reliability of interleukin-6 (IL-6) to diagnose IUI and early neonatal infectivity. The groups of patients are (A) pregnant women with regular term and (B) pregnant women with PTB, both, with ruptured amniotic membrane or with intact ones. The results of their infectious parameters are determined and analyzed: Leu number, CRP and IL-6 in mother's blood and newborn's blood. It is obvious that the highest percent of IUI is detected by using the blood level of IL-6, followed by CRP and Leu number. The most significant correlation is established between PTB and pathologic levels of IL-6 in cord blood (> or = 30 pg/ml, OR-40.09). In conclusion, we could summarize that IL-6 is a reliable parameter and sign for IUI in cases with PTB. It opens the door to a potential application of its laboratory testing, thus allowing a crucial decision with problematic therapeutic cases, when discussing the PTB.