A method for identifying specific cell populations with the computerized microscope is described. This method utilizes double staining techniques using immunofluorescent antibodies and the Feulgen technique. It was applied to measure the area and DNA content of the nuclei of beta-cells in patients with Persistent Neonatal Hypoglycemia with Hyperinsulinism (PNHH). A significant increase in the area and DNA content was found in nuclei of patients compared to a control group. This method may be applied to sample cells from other tissues as well.