A study has been made of the fine structure of hepatic parenchymal cells of human biopsy material in a case of pancreatic tumor with obstructive jaundice. Dense particles about 60 A in diameter have been found in the cytoplasm, which are considered to be ferritin molecules by electron microscopy. They are encountered throughout the cytoplasmic matrix and are often aggregated in electron-transparent areas, most of which are enclosed by an apparently single-layered membrane. Identification of the elemental iron has been pursued by the application of the x-ray scanning microanalyser which reveals a quantitative value within 1.0 per cent of the pure iron sample. The use of x-ray scanning microanalysis enables one to obtain accurate data from extremely small and precisely defined volumes of biological specimens.