We estimated the levels of interleukin 6 (IL-6) and neopterin, in serum of twelve nonpregnant (group A) and 28 pregnant women between 28-36 weeks of pregnancy. Group B consisted of eight patients with uncomplicated pregnancy, group C consisted of thirteen pregnant women with clinical signs of preterm labour and without laboratory markers of infection and group D consisted of seven pregnant women with signs of preterm labour and with laboratory markers of infection. The levels of IL-6 and neopterin were significantly higher in group D compared to groups A, B and C (p < 0.05). Similarly, the level of C-reactive protein (CRP) and total white blood cell count (the laboratory markers of infection) were significantly higher in group D than in groups A, B and C. Total white blood cell count was significantly lower in group A than in group B and D (p < 0.05). There were no significant differences in values of IL-6, neopterin and CRP between groups A, B and C (p > 0.05). In all groups, significant correlations were found between IL-6 and neopterin as well as total white blood cell count and CRP. Our results suggest that IL-6 and neopterin may be the markers of preterm labour caused by infection. On the other hand, cell-mediated immune response may be involved in the mechanisms of preterm labour.