Compositions and methods are provided for achieving in vivo islet cell regeneration in subjects with preexisting diabetes. The methods comprise short term treatment with a composition having a gastrin/cholecystokinin receptor ligand and an EGF receptor ligand. Treatment with such a composition for a short term resulted in a prolonged period of increased insulin release, decreased fasting blood glucose, and improved glucose tolerance, the prolonged efficacy, the period being considered from the time of cessation of treatment.