Cyclosporin ?A'' is the major component of the Cyclosporins, a group of nonpolar cyclic oligopeptides possessing immunosuppressive activity. Cyclosporin ?A'' is used extensively in the prevention and treatment of graft-versus-host reactions in bone marrow transplantation and for the prevention of rejection of kidney, heart, and liver transplants. As its role in transplantation surgery increases, the demand on industry to improved yields intensifies. In order to obtain and maintain a competitive economic position for new and existing fermentation respectively, it is also necessary to find means for increasing the yields of the fermentation product. The present study has been designed to enhance production capability of Cyclosporin ?A'' by local isolates of Aspergillus terreus by mutating the cultures with UV radiation and mutagenic chemicals.