Seven diabetic patients who had been dependent on insulin before pregnancy (classes B, C, D of White) threatened to go into premature labour between the 31st and 36th week of the pregnancy. They were treated by intravenous administration of Ritodrine, the dosage varying between 100 and 400 micrograms per minute. The changes in the mother consisted in a rise in the blood glucose level which rose from 140 +/- 34 mg % to 212 +/- 56 mg % (p less than 0.01). This occurred in spite of a mean rise of 49% of insulin (p less than 0.0025) and a moderate ketonuria in two patients and a severe acido-ketosis in two further patients. In five patients there were no effects on the fetus as far as repeated observations of the fetal heart rate could detect. On the other hand, in the two mothers who developed acido-ketosis during the transfusion the fetal heart rythm showed signs of acute fetal distress, which however was temporary. Oscillations were reduced and there were late decelerations. These disappeared when the maternal metabolic state was brought back to equilibrium. 13.1 +/- 7.3 days were gained for the fetus by using tocolytic treatment, and this is considered a success. Discussion of these cases is accompanied by a complete review of the literature of the administration of beta-mimetic drugs in diabetic women. The authors point out that special precautions have to be taken and special conditions have to be fulfilled when this type of treatment is used. These consist of changes in the amounts of insulin that are given and particularly careful observation of the fetal heart rhythm before and during treatment.