Several molecular techniques has been introduced recently for the differentiation of microbial isolates: plasmid profiles, restriction fragment length polymorphism of chromosomal DNA or plasmids, ribotyping, arbitrarily primed PCR, pulsed-field gel electrophoresis(PFGE), and phylogenetic analysis. Molecular strain typing became an essential tool for epidemiological investigation. And conventional serotyping or phage typing methods are so time-consuming and labor-intensive that molecular fingerprinting methods are used as a substitute. Clinical microbiology laboratory cannot help doing strain typing for infection prevention and control, and should make a good choice among them in respect of efficiency and cost effectiveness. (Korean J Clin Microbiol 1998;1(1):14)