The distribution of some metals in nuclei and nucleoli of normal and regenerating rat liver was determined. The contents of Co, Zn, Cu, and Mn in nuclei were less than 3% of those in whole cells. Cr and Ni, which are known carcinogens, were present in cells in much smaller amounts than the metals above, but their contents in nuclei were more than 20% of those in cells. All of these metals were retained in nucleoli; the contents in nucleoli, per milligram of protein, were 3 (Zn) to 18 (Ni) times those in nuclei.