A study was made of the pattern of 6 urinary estrogen fractions, from the twentieth week of pregnancy onward, in women with diabetes mellitus. These fractions were 2-methoxyestrone, estrone, ring D a-ketolic estrogens, estriol, 16-epiestriol and estradiol-17β (estradiol). As in normal pregnancy, 2-methoxyestrone behaved irregularly and frequently was not present in measurable amounts, particularly in urines containing large amounts of estriol. The excretion of ring D α-ketolic estrogen frequently was higher than has been found in normal pregnancy, and reached 16.2 mg per 24 hours in one case when corrected for experimental losses. During approximately weeks 35–37 of pregnancy, the mean corrected values (mg per 24 hours) for the various fractions in the urine of the diabetic patients were: 2-methoxyestrone, 0.40; estrone, 1.5; ring D α-ketols, 10.0; estriol, 24.7; 16-epiestriol, 1.0; and estradiol, 0.60. The excretion of the 6 fractions taken together and corrected for experimental losses was usually considerably higher than the excretion of total estrogens as measured by the Ittrich technique in the same urines.