In plasma obtained from seven mothers before, during, and after normal labor and delivery, catecholamine and cyclic nucleotide concentrations were investigated. Dopamine concentration showed a significant elevation on admission to hospital in labor and there were marked increases in norepinephrine and epinephrine concentrations during labor at 10 cm cervical dilatation and immediately after delivery, respectively. No significant change in dopa, cAMP, or cGMP was found during the experimental period. However, since the van Beaumont quotient (J.Appl. Physiol. 34, 102-106) for cAMP did not follow the reduction in plasma volume, the concentration appeared to rise during labor. Positive correlations were observed between epinephrine on one hand, and heart rate and systolic blood pressure on the other, as well as between norepinephrine and cAMP, respectively, during labor. The diminution of epinephrine on the fourth day postpartum might reflect a reduction of emotional stress concomitant with labor. cAMP was found to be quickly cleared from the bloodstream within 2 hours after delivery. These results suggest that plasma concentrations of epinephrine and cAMP, especially epinephrine, are indices of maternal psychological and physiological stress during labor and following delivery.