It has been suggested that the induction of ornithine decarboxylase (ODC) activity during pregnancy might contribute to the low ureagenic flux that enables the pregnant mother to spare nitrogen and support growth. Thus, we have studied the ODC activity, and urea and polyamine levels in livers of virgin and 21-day pregnant rats, either in a basal state or after the induction of ureagenesis by inducing diabetes in rats by streptozotocin injection. Diabetes led to a marked increase in circulating and liver urea levels in virgin rats. This response was significantly reduced in late-pregnant animals. Diabetes did not modify ODC activity in pregnant rats, which showed much lower activities than their virgin controls. Diabetes caused a depletion of the liver spermine content in pregnant rats. Spermidine levels were higher in both groups of pregnant animals than in their respective controls. Our results suggest first that the mechanisms contributing to spare nitrogen in the pregnant mother are likely to be present in diabetic pregnant animals and, second, that ODC does not mediate the metabolic adaptations leading to a low ureagenic flux and a higher nitrogen retention at the last stage of pregnancy.