Amniotic fluid concentration and content (amniotic fluid volume X concentration) of C-peptide and catecholamines (epinephrine, norepinephrine) and their interrelationship was studied in nine women with gestational diabetes, in 14 women with type I diabetes, and in 20 healthy control women between the thirty-sixth and thirty-ninth week of gestation. Mean amniotic fluid volume was significantly larger (p less than 0.05) in the type I diabetic group than in the control group. Mean concentration and content of amniotic fluid C-peptide were elevated in women with gestational diabetes, significantly so in women with type I diabetes (p less than 0.05) as compared with nondiabetic control women. Mean amniotic fluid catecholamine concentrations were lower, although not statistically so, in both insulin-dependent and gestational diabetic women than in control women. Mean amniotic fluid catecholamine content was higher, although not statistically so, in women with gestational diabetes than in control women. In the type I diabetic group, epinephrine content was significantly lower (p less than 0.05) and norepinephrine content significantly higher (p less than 0.05) than in the control group. A significant positive correlation between the content of norepinephrine and C-peptide was found in control women (r = 0.57; p less than 0.05) and in women with gestational diabetes (r = 0.75; p less than 0.05). The close interrelationship could indicate a parallel maturation of these two hormonal systems.