A study was conducted to compare bioavailability, interactions and retention of different sources of Zn and Cu fed to rats. Sixty-three male CD rats were fed individually a purified diet and deionized water ad libitum. The nine treatments included were all combinations of three Zn (ZnMet, ZnLys, ZnSO4) and three Cu (CuLys, CuSO4, CuO) sources added to the basal diet at 30 mg/kg of Zn and 6 mg/kg of Cu forming a 3' 3 factorial experiment. After the four-week supplementation phase, four randomly selected rats from each treatment were sacrificed (Phase 1). The remaining rats were fed the purified, unsupplemented diet for an additional week (Phase 2) and then sacrificed. Mineral (Zn and Cu) concentrations were determined in plasma, liver, kidney, bone and muscle, and metallothionein (MT) content was determined in liver and kidney. Plasma Cu concentrations were lower (p < 0.05) for CuO-than CuSO4- and CuLys-supplemented rats. Bone Zn concentrations were higher (p < 0.05) for CuLys-than for CuO-supplemented rats. In all tissues where Cu was measured, CuO was the lowest (p < 0.05) available source of Cu. Furthermore, in muscle, CuSO4-supplemented rats had higher (p < 0.05) Cu concentrations than CuLys-supplemented rats. Kidney MT concentrations followed the same pattern as Cu concentrations, with CuO-fed rats having the lowest (p < 0.05) MT concentrations. Plasma Cu concentrations of depleted rats were lower (p < 0.05) for CuO-than CuLys-supplemented rats. Kidney Zn concentrations were lower (p < 0.05) for CuSO4-than for CuO-supplemented rats after depletion. In liver, CuO supplemented rats had the lowest (p < 0.05) Cu concentration. Copper oxide was less available than CuLys and CuSO4 when added in adequate dietary levels. However, organic (ZnMet and ZnLys) and inorganic (ZnSO4) sources of Zn were similar.