Removal of the spleen in albino rats free from Bartonella muris infection is followed by an increased elimination of copper in the feces, which commences 2 weeks after splenectomy. This is associated with a persistent negative copper balance. An increased retention of iron occurs during a period of 4 to 6 weeks after splenectomy with a return of the iron metabolism to normal after this period. No disturbance in creatine or creatinine metabolism occurs. The uric acid amount is unchanged. There is an increase in the retention of nitrogen, which is first noted 3 weeks after splenectomy. The spleen is essential for the utilization of copper in the body.