Abstract: There are disclosed metallic colloid particles containing platinum fine particles wherein platinum colloid particles are supported on the surfaces of gold colloid particles, and the platinum fine particles have an average particle diameter of at most 5 nm; a process for producing the metallic colloid particles; a metallic corpuscular carrying body wherein the above metallic colloid particles are supported on a carrier and a process for producing the carrying body. The resultant metallic colloid particles, which have higher sensitivity, are well suited as a label for immunological measurement and protein-staining agent for various proteins.