The concentration of dopamine (DA), norepinephrine (NE), and its metabolites 3-methoxy-4-hydroxy-phenylethylene glycol (MHPG) and vanillyl mandelic acid (VMA), and prostaglandins E2, and F2a in amniotic fluid were measured at labor (1-3 cm of cervical dilatation), in uncomplicated and complicated pregnancies. The amniotic fluid concentration (mean +/- SD) of MHPG in maternal smoking (S) (30.6 +/- 11.9 nmol.mg creatinine-1) and intrauterine growth retardation (IUGR) (36.7 +/- 15.2 nmol.mg creatinine-1) groups is significantly higher than in uncomplicated pregnancies (C) (22.9 +/- 8.8 nmol.mg creatinine-1), or diabetes mellitus groups (D) (26.1 +/- 10.9 nmol.mg creatinine-1) groups; VMA presents similar differences between groups S (145.8 +/- 84.4 nmol.mg creatinine-1) and IUGR (173.0 +/- 135.4 nmol.mg creatinine-1) higher than C (58.3 +/- 26.1 nmol.mg creatinine-1) and D (76.8 +/- 49.0 nmol.mg creatinine-1) groups. NE levels differ between groups in a similar way, but DA does not present significant differences between groups. Prostaglandin levels are higher in the S than in the C group. Nicotine action and/or hypoxia are proposed as a possible cause of NE, MHPG, and VMA rise in amniotic fluid of S, and IUGR versus C or D groups.