Three staining techniques--Hellerström-Hellman alcoholic silver nitrate, pseudoisocyanin, and the immunofluorescent technique for somatostatin--were compared to determine whether they are staining the same cell in the pancreatic islet of the rat. These comparisons were made by using staining and restaining procedures on the same islet. The results demonstrate that all three procedures stain the delta cell of the rat pancreatic islet. Some advantages of using pseudoisocyanin are discussed.