Serum trace elements were measured serially during 27 chemotherapeutic episodes in 22 patients undergoing chemotherapy for acute myelogenous leukemia. Serum copper, zinc, selenium and bromine were measured twice weekly by PIXE for a period of 3–20 weeks. Serum bromine dropped dramatically to very low values during the weeks following chemotherapy and returned slowly to subnormal values only after a few months. Serum zinc sharply decreased in cases of life-threatening infection and patients with persisting low values generally went to death. Serum copper followed fibrinogen evolution with fairly good accordance, while serum selenium showed less systematic effects.