Family studies of rare LW(a-b+) propositi confirm the recent finding based on frequency studies that the LW blood groups are polymorphic in Finland (Sistonen & Tippett, 1982); they are controlled by two alleles LWa (0.97) and LWb (0.03) independent from most other common blood group loci. Lod scores for LW and the loci for 27 markers are presented.