Optical properties of gold and silver nanoparticles are considered. Processes of preparation of these particles are described. The data presented about application of these nanoparticles in immunoagglutination assays. The features of these metals in immunoagglutination assays are compared. Application of gold nanoparticles in DNA hybridization assays is presented. Application of these metals in cell imaging and therapy is considered. Other prospective metal and semiconductor composites for application in these area are considered.