The effect on Bartonella muris anemia of adding copper or iron or both to an adequate diet was studied. The addition to the diet of copper (0.1 mg. per rat per day), or iron (1 mg. per day), or both during a period of 2 days prior to splenectomy and 1 month subsequent thereto failed to protect adult albino rats against Bartonella muris anemia. The addition of copper to an adequate diet for a period of 10 days prior to splenectomy and 1 month subsequent thereto protected 75 per cent of the rats against the anemia. The addition of iron (1 mg. per rat per day) for a period of 10 days prior to and 1 month subsequent to splenectomy protected 50 per cent of the rats against this anemia. The addition of both copper and iron for a period of 10 days prior to and 1 month subsequent to splenectomy protected 75 per cent of these rats against Bartonella muris anemia. The addition of copper alone for a period of 2 months prior to and 1 month subsequent to splenectomy protected 63 per cent of the rats against Bartonella muris anemia. The addition of iron, or of both copper and iron during a period of 2 months prior to splenectomy and 1 month subsequent thereto protected about one-third of the rats against Bartonella murisanemia.