Laboratory Corporation of America Holdings, more commonly known as LabCorp, is an American S&P 500 company headquartered in Burlington, North Carolina. It operates one of the largest clinical laboratory networks in the world, with a United States network of 36 primary laboratories. Before a merger with National Health Laboratory in 1995, the company operated under the name Roche BioMedical. LabCorp performs its largest volume of specialty testing at its Center for Esoteric Testing in Burlington, North Carolina, where the company is headquartered. LabCorp was an early pioneer of genomic testing using polymerase chain reaction (PCR) technology, at its Center for Molecular Biology and Pathology in Research Triangle Park, North Carolina, where it also performs other molecular diagnostics. It also does oncology testing, human immunodeficiency virus (HIV) genotyping and phenotyping. LabCorp also operates the National Genetics Institute, Inc. (NGI) in Los Angeles, California which develops PCR testing methods. LabCorp's ViroMed facility, originally in Minnetonka, Minnesota until closing this site in 2013, is now housed in Burlington, NC and performs real-time PCR microbial testing using laboratory-developed assays. LabCorp also provides testing in Puerto Rico and, outside the United States, in three Canadian provinces.