Results of a population study with all currently available B-cell specific alloantisera indicate that eight antigens controlled by the RhLA-linked DR locus can now be identified. This leaves a gene frequency of about 0.15 for unidentified or "blank" antigens of that locus. Of the nine identifiable Ia antigens which are not controlled by the DR locus, three or four may form the basis of a second series which is probably also controlled by the RhLA region.