Zinc (Zn) plays an important role in the maintenance of immune functions, including cellular/humoral immunity, and in the prevention of oxidative injury. Therefore, the maintenance of a normal Zn status may be important in bone marrow transplantation (BMT) patients. Serum Zn levels were determined in 35 children during the BMT period. In addition, as Zn-related factors, serum Cu levels and alkaline phosphatase (AP) activity were also measured. There was a significant decrease in Zn and AP values during the immediate post-transplant period (lowest at day +7) when compared to pre-BMT levels (p <.01). The patients who developed hypozincemia were more likely to be transplanted for a diagnosis of malignant disorder and were younger, and adverse events appeared to occur more frequently. This preliminary study suggests that maintaining a normal Zn status may be important in BMT patients and that Zn deficiency may be a risk factor for adverse events.