Tetrameric immunoglobulin (lg) in most teleosts is a fully disulphide cross-linked molecule. The multimeric lg from four species from the order Gadiformes; haddock (Melanogrammus aeglefinus L.), Atlantic cod (Gadus morhua L), pollock (Pollachius pollachius L.) and tusk (Brosme bromse A.) was examined by denaturing, non-reducing gel electrophoresis and gel filtration chromatography. Despite having a native molecular mass equivalent to that of other tetrameric teleost lg, gadid lg was never observed to exist as a fully disulphide cross-linked molecule; existing instead as a covalently cross-linked trimer with a non-covalently associated monomer. It is unknown whether this unique cross-linking is associated with the limited or absent specific humoral responses reported for members of this order.