Corticotropin-releasing factor-binding protein (CRF-BP) in pregnant women is measurable in maternal and fetal plasma as well as in amniotic fluid. The concentration of CRF-BP in maternal plasma and amniotic fluid changes significantly at the time of parturition. The aim of the present study was to evaluate fetal plasma CRF-BP levels in women delivering at term or with preterm labour. CRF-BP levels were measured the in umbilical cord plasma of women subdivided into two groups: (1) healthy pregnant women throughout the last 5 weeks of pregnancy either (a) out of labour (n = 21) or (b) at delivery after spontaneous labour (n = 64); and (2) patients with preterm labour (a) gone to delivery (n = 12) or (b) responding to tocolysis (n = 10). In the group of healthy women at term, CRF-BP levels were also measured in maternal plasma. CRF-BP was measurable in all specimens of umbilical cord plasma. Mean values +/- SEM at 40 weeks (5.85 +/- 0.65 nmol/l) were significantly lower than those obtained at 37 (6.48 +/- 0.47 nmol/l) or 38 (6.95 +/- 1.16 nmol/l) weeks of pregnancy. Similarly, mean +/- SEM maternal plasma CRF-BP levels in women at term out of labour were lowest at 40 weeks (3.57 +/- 0.22 nmol/l). In these women, mean +/- SEM CRF-BP levels in cord plasma (37 weeks: 6.47 +/- 0.47; 38 weeks: 6.95 +/- 1.16; 40 weeks: 5.85 +/- 0.65 nmol/l) were significantly higher than in maternal plasma at the same gestational age (37 weeks: 4.29 +/- 0.2; 38 weeks: 4.35 +/- 0.205; 40 weeks: 3.57 +/- 0.22 nmol/l). Mean +/- SEM levels of cord blood collected at delivery at term (4.93 +/- 0.14 nmol/l) showed lower CRF-BP levels than in women out of labour (6.18 +/- 0.55 nmol/l). Patients with preterm labour, with delivery within 48 h, showed significantly lower levels of cord plasma CRF-BP (4.21 +/- 0.29 nmol/l) than women at term out of labour (6.18 +/- 0.55 nmol/l) and than those at term with labour (4.93 +/- 0.14 nmol/l). Cord plasma CRF-BP levels decreased in the last 5 weeks of pregnancy, similar to maternal plasma CRF-BP levels, the lowest values resulting in women at labour or with preterm labour, thus suggesting that changes of CRF-BP in cord plasma are associated with the events of parturition.