Since the introduction of the polymerase chain reaction, nearly all the molecular biomedical scientists around the world take advantage of it nearly everyday. Recent advances include the further development of single-stranded conformational polymorphisms, the conjunction of the "Pyrococcus furiosus" DNA polymerase to amplify its fidelity, the use of the different fluorescence-labeled primers to make bands visible by UV-transillumination, and the use of a reverse transcriptase polymerase chain reaction extending its field beyond the study of RNA. Nowadays, the capability of studying a single target molecule allows technology to be applied to single sperm typing, pre-implantation diagnoses, fetal cell analysis within maternal circulation, detecting circulating cancer cells, diagnosis of mitochondrial disorders, study of infectious diseases and the detection of residual diseases after treatment of leukemia and lymphoma.