Clinical, haematological and biochemical aspects of a new family with heterozygous haemoglobin Presbyterian [beta 108 (G 10) Asn----Lys] are described. It could be readily separated by isoelectric focusing, DEAE-cellulose chromatography and by cation exchange high-performance liquid chromatography (HPLC). The characterization of this mildly unstable haemoglobin was made by reverse-phase HPLC. This is the fourth family with Hb Presbyterian so far described.