The radioactivity can be detrimental to the human being. It is hazardous to hemopoetic system, mucous membranes etc.. Through its effect on genes, it can be carcinogenic. Its therapeutic uses can cure human beings, e.g.: tumor suppression & solid tumor therapy. Its detection can be done by radiation detectors & can be quantified (gas ionization detectors, scintillation detectors). The study used in laboratory medicine for diagnostic purposes, e.g. radioisotopes in radio-immunoassay (RIA) for detection of very small amount of substance & with high degree of accuracy. In hematology, blood cell life span & blood volume kidney function tests. RIA is commonly used for different hormonal assays as well as tumor markers detection & quantity. Radioisotopes have many useful roles in clinical laboratory in both chemistry and hematology as in radio-immunoassay; it is used for detection of very small amount of substance with high degree of accuracy. Radioisotopes have also role in hematology; it is used in vivo studies, involving the labeling of cells in the blood or bone marrow, in measurement of blood volume, in measuring the splenic red cell pool in ferrokinetics, in measurement of blood loss from the gastrointestinal tract using 51Cr in measurement of platelet life-span and red cell life span. Immunoassays can be classified into labeled as particle agglutination immunoassay, radio-immunoassay, enzyme immunoassay, fluorescent immunoassay and chemiluminescent immunoassays, and unlabeled immunoassay as precipitation immunoassays.