Maternal serum cortisol (F) and prolactin (PRL) levels were measured during labor in 20 uncomplicated pregnancies. Four pregnant women were admitted with ruptured membranes (RM group) and 16 were admitted with intact membranes (IM group), ten with spontaneous onset of labor (SL group) and 10 with induced labor (IL group), five with a prolonged for duration labor (PL group) and 15 with a normal for duration labor (NL group). Before the inset of labor F levels were statistically higher (p less than 0.05) in the RM group (x = 975 ng/ml), than in the IM group (x = 664 ng/ml), and also in the SL group (x = 783 ng/ml), than in the IL group (x = 679 ng/ml). During labor, in all twenty pregnant women a marked rise of F (from x = 726 ng/ml before the onset of labor, to x = 911 ng/ml) and a marked fall of PRL (from x = 161 ng/ml to x = 122 ng/ml) were observed (p less than 0.05). In the PL group the F elevation and the PRL drop were more pronounced (p less than 0.001). After placental separation, PRL levels increased slightly while F values remained unchanged. These changes in hormone levels before and during labor could be attributed to the emotional and physical stress of labor.