The relationships among maternal anxiety, selected stress-related biochemical factors, and progress in three defined phases of labor were determined for 32 married, normal, primigravid women, 20 to 32 years of age. Comparisons of plasma epinephrine, norepinephrine, and cortisol in third-trimester pregnancy, during labor, and after delivery are provided. At the onset of Phase 2 of labor (3 cm. of cervical dilatation), self-reported anxiety and endogenous plasma epinephrine are significantly correlated. With the deletion of subjects to control for the effect of medications, higher epinephrine levels are significantly associated with lower uterine contractile activity at the onset of Phase 2 and with longer labor in Phase 2 (3 to 10 cm. of cervical dilatation). The relationship between epinephrine and progress in labor is explained by an adrenoreceptor theory.