Fish has relatively poor antibody response compared to mammals, though there is considerable variety among different fish species. Atlantic cod (Gadus morhua L.) can be classified as a low responder, as pre-immune sera has a similar antibody titer to given antigens as immune sera. Still, the Atlantic cod has an immunoglobulin gene repertoire comparable to other teleost species, and three families of immunoglobulin heavy chain variable genes (VH-genes) have so far been cloned and sequenced (Bengten et al., 1994). We want to study the regulation and expression of the Atlantic cod immunoglobulin genes, as this particular species differs in the antibody response to both soluble and particulate antigens. A cDNA library from the head kidney of cod was screened with the known immunoglobulin genes as probes (VH and CH) in search of additional VH-gene families. The results from the present sequencing work will be presented.