Unusual expression of interleukin-1alpha, -1beta and -6 was previously found in the epiphyseal cartilage of rat fetuses prenatally exposed to various non-steroidal anti-inflammatory drugs (NSAID, i.e., ibuprofen, piroxicam, tolmetin) and selective cyclooxygenase-2 inhibitor (DFU). The aim of the present study was to evaluate the role of placenta in such phenomenon. Morphology of the organ, thickness of basal and labyrinth layer, immunoexpression of COX isoenzymes were examined, and confronted with maternal biochemical data and fetal developmental parameters. Higher maternal urea level, as well as lower placental weight and labyrinth thickness were found in the group of fetuses who revealed expression of genes coded the selected interleukins, when compared with the xenobiotic-exposed pups without the selected genes expression and untreated control. A significant correlation between placental weight and maternal total protein or urea level was revealed. Histological changes like inflammatory infiltration and calcification were observed sporadically. Location and intensity of COX-1 staining was similar in all cases. However, more intense COX-2 staining for majority of cells of the basal zone and in dispersed giant cells of the labyrinth was found in inflamed organs. It could be concluded that abnormal expression of the selected interleukins is associated with low placental weight and decrease of its thickness, especially labyrinth zone, as well as with high maternal urea level.