In a clinical study the course of cortisol concentration in serum was investigated at the following points: under labour, directly post partum simultaneously in the mother, the umbilical artery and vein and on the first and second day after birth in the mother and on the second third days in the newborn. Two groups of patients were investigated: 51 first and multiple parturients with peridural fentanyl analgesia for labour pain relief (PFA) and 42 first and multiple parturients as control group. The reduction of stress under PFA could be confirmed by measurement of cortisol concentrations in serum. The cortisol concentrations listed according to the time of day showed significantly lower values for the multiple parturients compared with the control group. Circadian peaks of the intrapartal cortisol in serum are generally absent in the multiple parturients. In the first parturients of the PFA group a more differentiated course of the cortisol levels listed according to the time of the day was observed. Up to about noon, the cortisol values are markedly lower than those of the control group, but after decreasing tendency in the early afternoon, they show another peak around 4.00 p.m. This means there is still a circadian rhythm under the influence of PFA for the first parturients. In contrast to the multiple parturients, the reaction of the cortisol level of the first parturients after PFA is only of short duration. At the other measuring points there are possibly different stress factors such as permanent expectation under labour and the absence of labour experience, superposing the fentanyl effect seen in the cortisol levels of the multiple parturients.