Application of trivalent chromium (daily 1 mg, p.o.) to pregnant rats in the time of gestation and thereafter--beginning with the first day of the gestation and lasting for 50 days--did not change the i.p. glucose tolerance of the adult animals. The insulin concentration in serum 30 min after glucose loading was decreased significantly. The basal concentration of serum insulin of neonates was diminished, too. The insulin content of the whole pancreas was decreased in mother animals and increased in neonates. Secretion of insulin by isolated islets of the neonatal animals was unchanged. Insulin biosynthesis of the islets of these animals was increased in presence of 6 and 15 mM glucose, respectively. These data suggest an effect of trivalent chromium on endocrine pancreas.