Abstract.Molecular cloning methods and strategies which have been employed to reveal the exact nature of antibodies (immunoglobulins) and major histocompatibility complex (MHC) antigens from Atlantic salmon,Salmo salarL., have been discussed briefly. As in other fish species, the immunoglobulin heavy chain (IgH) of the Atlantic salmon has the typical characteristics of the IgM heavy chain from higher vertebrates. The membrane form of IgH is somewhat special, as the mRNA splicing pattern excludes the fourth constant exon, generating a membrane‐anchored IgM one domain shorter than the mammalian counterparts. This splicing pattern has also been reported from cod and catfish, and seems to be general for teleosts. Notably, Atlantic salmon possess two isotypic IgM heavy chain constant region genes. The presence of two closely related IgH genes is in accordance with the quasi‐tetraploid state of the Atlantic salmon genome, which means that the entire gene complex is probably duplicated. As deduced from phylogenetically conserved amino acid residues and the pattern of polymorphic residues, MHC antigens from Atlantic salmon seem to parallel those from higher vertebrates. Improvement of disease resistance in aquaculture stocks is discussed in relation to MHC polymorph