The amino acid sequence of serum amyloid A (SAA) protein from mink was established by characterization of peptides derived from digestion of the protein with trypsin and from cleavage with BNPS-skatole. In three positions, two amino acid residues were found, showing that the protein is polymorphic. In position 10 both valine and isoleucine were found, while only valine was observed in protein AA. Prominent sequence homologies with protein SAA and protein AA from other species were seen, particularly corresponding to the segment between positions 31 and 54, but also in the C-terminal part of protein SAA, which is not shared by protein AA.