A sample of the Isle of Man population was tested for the following red cell antigens, serum proteins and red cell enzymes: ABH; MNSs He; Cc CwD Du Ee Ce; K k Kpa Kpb; Lua; P1; Fya Fyb; haptoglobin; transferrin; Ag; acid phosphatase; phosphoglucomutase; adenylate kinase; esterase D; adenosine deaminase and 6-phosphogluconate dehydrogenase. The study comprised 219 blood donors, 338 secondary school children and 116 females attending the only antenatal clinic. The results were studied for intra-island variation and for their their relationship with other Irish Sea Basin populations. The total sample results were compared with data for England, Cumbria, Eire, Northern Ireland, S.W. Scotland and Wales using a genetic distance measure.