The beta cells within the pancreatic islets are responsible for production of insulin, a peptide hormone required for maintaining normoglycemia. The establishment of efficient gene transfer into pancreatic islets is very important for studies of insulin and glucagon production and secretion, as well as for gene therapy purposes for the treatment of diabetes. We describe here in detail a protocol for adenoviral gene transfer into isolated mouse islets of the pancreas. Effective gene transfer into pancreatic islets using recombinant adenoviruses can be achieved with a multiplicity of infection (MOI) of 10. However, if the islets are not dispersed, adenoviral gene transfer is limited only to the cells on the periphery of the islets, which represent the glucagon-producing alpha cells in rodents. Dispersion of pancreatic islets with EGTA increases the efficiency of gene transfer into the cells within the core of the islets, which consist of insulin-producing beta cells.