The 95 % pancreatectomized female rat shows a progressive decrease in fertility with time elapsed since operation, finally resulting in sterility. This decrease appears in prediabetes, before the alterations in carbohydrate metabolism, and the presence of hyperglycemia aggravates them. A high percentage of exposed rats are not inseminated, and this number increases with the time elapsed since the operation and blood sugar level. At Cesarean sections, the uteri of some inseminated rats contained fetuses, whereas those of others were empty. Many of the fetuses found were dead. Lack of insemination, decreased number of ova, and high rate of fetal mortality explain the reduction in fertility and living newborns. These problems could be explained by the metabolic and pathological changes found in ovaries and uterus. In the diabetic female rat a sexual hormonal alteration probably exists which could help explain these symptoms. The possibility of quantitative or qualitative modifications in gonadotropins or estrogens, an imbulance or blockage of these hormones should be considered. 1 Supported by Grant No. 2305 from the Consejo Nacional de Investigaciones Científicas y Técnicas and by Grant M 66.0126 from the Population Council