Serial plasma, amniotic fluid, and urine samples were analyzed for epinephrine (E) and norepinephrine (NE) in eight subjects during midtrimester abortion induced by intra-amniotic prostaglandin F2alpha (PGF2alpha). After PGF2alpha administration, plasma E increased and there was no change in plasma NE levels. Amniotic fluid levels of E and NE decreased initially. During the course of abortion the mean level of E in the amniotic fluid increased after fetal distress and decreased after fetal death, indicating that the midtrimester fetus of both E and NE increased following PGF2alpha. The observation that mean plasma levels and urinary excretion rate changes correlated better with the course of abortion and uterine contractility rather than with the time of PGF2alpha administration was consistent with the hypothesis that the catecholamine response may be due to the stress of labor rather than to the PGF2alpha per se.