Neurokinin B (NKB) is a neuropeptide belonging to the family of tachykinins-related peptides that elicits contractility of human myometrial strips in vitro. The present study evaluates whether placental mRNA and peptide expression of NKB change in women at preterm labor.A group of 26 women with singleton pregnancies were enrolled in the study. Placental tissue specimens were collected from pregnant women delivering after elective cesarean section, after labor at term, or after preterm labor. Changes in placental NKB mRNA and protein expression were evaluated by real-time quantitative RT-PCR analysis and by immunofluorescence respectively.Placental mRNA expression of NKB was significantly higher after term and preterm labor (P<0.001) than cesarean section, and highest after preterm labor. Immunofluorescent staining in placentas from preterm or term labor was more intense than after cesarean section (P<0.001). In particular, NKB protein expression was higher in placentas collected after preterm labor than those collected after term labor.Neurokinin B mRNA and protein are highly expressed in placenta at term and preterm labor; thus, the involvement of this neuropeptide in the events cascade leading to parturition may be suggested.