Hepatocyte age was estimated from its distance from the portal tract. We have previously shown that hepatocytes are formed adjacent to the portal tract and stream toward the terminal hepatic vein, advancing at a daily velocity of 2 μm. Thus, the farther a cell from the portal tract, the older it is. This relationship between cell age and distance served here for the study of age-dependent changes in the hepatocyte, particularly nuclear area and DNA content. DNA content was derived from the absorbance of Feulgen-stained nuclei in 5-μm-thick tissue sections. Absorbance and nuclear area were measured with a cytophotometer. Since most nuclei of the tissue section were sliced, DNA content was estimated also in intact nuclei which were sampled by fine needle aspiration, and stained with either Feulgen or propidium iodide. Feulgen-stained nuclei were scanned by a cytophotometer, while the DNA content of propidium iodide-stained nuclei was measured by flow cytometry. Absorbance was expressed in relationship to the mean absorbance of diploid periportal littoral cells. Littoral absorbance was delined as one absorbance unit. A high correlation between nuclear absorbance and area was observed in nuclear suspensions (adjusted r-square 0.79), so that nuclear area may serve as a good predictor of nuclear DNA content, which is valuable in routine sections which are stained with H and E. Most periportal hepatocytes were polyploid and their mean absorbance was 1.68 units. Nuclear absorbance increased with cell distance from the portal tract. Within 100 pm it rose from 1.68 to 1.92 units. Nuclear area increased by 13%. Since the cell covers the 100 pm distance in 60 days, its absorbance increases daily by 0.006 units. Yet since the advancing hepatocyte gets older as it advances, nuclear absorbance increases with hepatocyte age, and so does nuclear area.