The murine monoclonal antibodies BS58 and R6A are known to recognize epitopes related to the human Rh system: neither antibody reacts with Rhnull cells and the BS58 antigen is not expressed by‐D‐or ·D· cells. It is shown here that the numbers of BS58 and R6A antigen sites vary with Rh phenotype. Both epitopes are well represented on cells of the CDe/CDe, CDe/cDE and CDe/cde phenotypes; BS58 sites are markedly reduced on cde/cde and cDE/cde and are only just detectable on cDE/cDE cells when compared with R6A sites. The number of R6A sites per red cell ranged between 20,000 and 150,000. The evidence indicates that the BS58 epitope is not on the polypeptides carrying D or R6A, nor is it uniquely on one of the polypeptides carrying either C, c, E or e. It is suggested that the BS58 epitope is either common to all the CcED polypeptides or that it is present on a polypeptide which has not yet been identified biochemically.

NIM-M8 is a monoclonal IgM antibody, specific for the LWab antigen as shown by its reaction with red cells of all donors except those lacking LWa, LWb and LWab. Indirect immunofluorescent staining and cell sorter analyses have shown that LWab is present on a subpopulation of human lymphocytes. Cell fractionation studies indicate that subsets of both B and T cells express LWab and it may, therefore, provide a further marker for heterogeneity in these lymphocyte populations.

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.

An exclusion mapping method is described which attempts to combine in a compact form negative information from deletion studies and studies on families segregating for existing reference markers, centromere markers and familial translocations. A meiotic map is provided for exclusion mapping. Chromosome 22 is used as a worked example of the exclusion mapping of the MNSs blood group. A particular assignment for MNSs to the q28 or q31 region of chromosome 4 is suggested by this method.