Albumin Canterbury is a fast-migrating variant of human albumin. It constituted 50% of the total serum albumin in two unrelated New Zealand males. Two-dimensional tryptic mapping suggested that the mutation occurred between residues 313 and 317 inclusive. This was confirmed by mapping of S. aureus V8 proteinase digests. The expected neutral peptide Ser-Lys-Asp-Val-Cys-Lys-Asn-Tyr-Ala-Glu (312-321) was missing and was replaced by an acidic peptide Ser-ASN-Asp-Val, Cys, Lys, Asn, Tyr, Ala, Glu. The mutation of 313 Lys----Asn, which occurs in the second domain of albumin Canterbury, does not alter the thyroxine (T4) or T3 binding. There was no discernible physical handicap associated with the presence of this new albumin.