Metal compounds provide new opportunities for building structures with defined properties. A number of diseases and their treatment dependent on the metabolism of inorganic constituents. The advances in inorganic chemistry provide better opportunities to use metal complexes as therapeutic agents. The mode of action of metal complexes on living organism is differing from non metals. These complexes show a great diversity in action. Metal coordination to biologically active molecules can be used to enhance their activity. This paper reviews about the various applications of metal complexes in biological system.