Abstract. The interleukin 4 induced 1 (IL4I1) gene, also known as FIG1, encodes a lysosomal protein in B cells with L-amino oxidase (EC 1.4.3.2) property and a high preference for aromatic amino acid substrates implicating a fundamental role in antigene processing and presentation (MANSON et al. 2004). In human, IL4I1 has been assigned to chromosome 19q13.3-19q13.4, a hot spot for susceptibility to several autoimmune diseases (CHAVAN et al. 2002). Based on comparative genome data between human and cattle (GOLDAMMER et al. 2002), an assignment of IL4I1 to Bos taurus chromosome 18 (BTA18) has been predicted within a quantitative trait locus for somatic cell score (KÜHN et al. 2003). This prediction is supported by the putative bovine sequence for IL4I1, LOC520692, which has been assigned to BTA18 close to 56.1 megabases within the annotated bovine sequence (NCBI build Btau-4.0). Therefore, we started positional cloning of bovine IL4I1, as a candidate gene related to adaptive immunity, i.e. during udder infections in cattle. Here we present the physical assignment of the bovine IL4I1 gene by fluorescence in situ hybridization (FISH) and radiation hybrid (RH) mapping.