Fifteen insulin-dependent diabetic (White's class B-C) and 10 healthy pregnant women were examined from the 12th to the 36th wk. Every 4 wk, a blood sample was drawn to determine total estriol, progesterone, placental lactogen and prolactin. Throughout the pregnancy, total estriol and progesterone in diabetic and non-diabetic women are very similar. On the contrary, the PRL levels are constantly lower in diabetic pregnant women, even though the difference is statistically significant only for the 24th wk determination. The hPL level is instead significantly lower in diabetic pregnant women at the 12th, 20th, 24th, 32nd and 36th wk. A negative correlation exists between the hPL value and the mean blood glucose level, performed the same day as the hormonal test. This correlation is statistically significant at the 12th, 16th, 20th, 28th and 36th wk. No significant difference is found between the two groups examined for the delivery week, the placental weight, the birth weight and the fetal body weight index. To conclude, while estriol and progesterone are not affected by the higher variability of glucose levels during pregnancy in diabetics, compared to normals, hPL and perhaps also PRL may be influenced by the mild hyperglycemia consequent to diabetes.