Copper deficiency was found in an adult patient who had received excessive daily oral zinc for 10 mo. The deficiency was characterized by hypochromic-microcytic anemia, leukopenia, and neutropenia. Although initially thought to be caused by iron deficiency, the anemia did not respond to oral or intravenous iron. Cessation of zinc tablets and ingestion of an oral copper preparation daily for 2 mo failed to correct the anemia or leukopenia. It was not until shortly after intravenous administration of a cupric chloride solution during a 5-day period, at a total dose of 10 mg, that serum copper and ceruloplasmin levels increased and the anemia, leukopenia, and neutropenia resolved. These data suggest that the elimination of excess zinc is slow and that, until such elimination occurs, the intestinal absorption of copper is blocked.