SummaryMultiple, superimposed Type I interferon (IFN) restriction fragments were resolved following 72–92 h of horizontal electrophoresis. Restriction fragment length polymorphisms (RFLPs) for α IFN (IFNA), β IFN (IFNB), ωIFN(IFNW) and trophoblast IFN (IFNT) genes were identified inHindill, Eco RI andTaqldigestions from 313 cattle. RFLPs with codominant segregation in cattle pedigrees were considered alleles, and 19 distinct polymorphic Type I IFN loci (5IFNA, 4IFNB, 8IFNWand 2IFNT) were identified. Allele frequencies and observed heterozygosity values were calculated for each locus and several loci were considered highly informative for linkage analysis. Bovine IFN gene numbers (10IFNA, 6IFNB, 20IFNWand 6IFNT) were estimated from the number of polymorphic loci plus additional monomorphic hybridizing bands present inEcoRI and Hindlll digestions. Physical linkage of the Type I IFN gene families on bovine chromosome 8 was demonstrated by pulsed field gel electrophoresis (PFGE). Hybridization of two or more IFN probes to similarly sized PFGE fragments suggested the tentative gene family order:IFNA/IFNW‐IFNT‐IFNB.These studies provide a basis for the development of more detailed genetic and physical maps of the bovine Typ