FMO4(Flavin-containing monooxygenase 4) also known as FMO2, FORMERLY or FMO, ADULT LIVER FORM, is an enzyme that in humans is encoded by the FMO4 gene. By PCR analysis, Dolphin et al.(1992) mapped the FMO4 gene to chromosome 1. Southern blot hybridization with single exon probes demonstrated that human FMO4 and FMO1 are, in each case, the product of a single gene. Lawton et al.(1994) proposed a reclassification of mammalian FMOs. Under this system, FMO2 described by Dolphin et al.(1992) is now designated FMO4.