Dehydroepiandrosterone sulphate (DHEA-S), estradiol (E2), estriol (E3), progesterone (P4) and cortisol (F) maternal plasma concentrations were determined using enzyme or fluoroimmunoassays in 28 healthy pregnant women prior to the induction of labour, performed for various reasons, in order to evaluate their impact on cervical ripening. Mean maternal and gestational ages were 24.7 +/- 3.6 years and 39.1 +/- 1.9 weeks, respectively, and the gravidity ranged from 0-4. The subjects were divided according to cervical maturity into Group A (n = 13, Bishop scores>> 4) and Group B (n = 15, Bishop scores < 4). There were no statistically significant differences observed between the two groups as to concentrations of oestradiol, oestriol, progesterone and cortisol. However, significantly higher concentrations of DHEA-S were found in group A compared to group B (1335 +/- 885 ng/ml and 558.2 +/- 191.4 ng/ml, respectively), (p < 0.001). In conclusion, the high DHEA-S concentrations in maternal plasma may play an important role in pregnancy by producing favourable cervical conditions for delivery or by triggering the labour itself.