Eleven elements in ten organs and tissues of mice fed with Zn-deficient diet (Zn-def. mice) and those fed with control diet (control mice) were determined by INAA. Zinc concentrations in the organs of Zn-def. mice were not distinctly lower than those of control mice except for bone and pancreas, as similar to the predecessors' reported results. However, the Co content increased significantly in all the organs and tissues of Zn-def. mice compared with control mice. The organs and tissues observed were histologicaly normal and no typical symptoms of Zn deficiency disease were recognised. The results suggest that the change of Co-concentration may be regarded as a mark of the prestage for a Zn deficiency disease.