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A 'new rare blood group antigen R1a (Rosenlund) is reported. The antigen is present in about 1 in 900 Norwegians. Nine unrelated R1(a+) people were found. Studies of seven families, leading to the discovery of 20 additional R1(a+) people, indicated the antigen is inherited as a Mendelian dominant character. Independent segregation was demonstrated between Rla and the ABO, MNSs, Rh, Lutheran, Duffy and Kidd blood group systems, the ABH secretor genes, and sex. The R1a antigen is inactivated by papain treatment. The corresponding antibody, anti-R1a, has so far been found in three sera that also contain antibodies to other rare blood group antigens.

The IgG subclass distribution of anti Rh antibodies (anti-D, 'anti-Du', anti-c, anti-E), anti-Kell and anti-Duffy (anti-Fya) antibodies was measured by two haemagglutination techniques on microtitre plates. The first technique involved rabbit subclass specific antisera which were used to agglutinate red cells previously reacted with the patients' antibodies at high concentration. The second, which was more sensitive, had an additional step by introducing sheep anti-rabbit antibodies (sandwich technique). By the sensitive sandwich technique we revealed, for anti-D antibodies: IgG1 8/19, IgG3 1/19, IgG1/IgG3 8/19, IgG1/IgG2/IgG3/IgG 41/19, IgG1/IgG4 1/19; for the Du reactive anti-D antibodies: IgG1 1/8, IgG1/IgG3 1/8, IgG1/IgG3/IgG4 6/8; for the anti-E antibodies: IgG1/IgG2/IgG4 2/3, IgG1/IgG2/IgG3/IgG4 1/3; for the anti-c antibodies: IgG1 2/5, IgG3 1/5, IgG1/IgG3 1/5; for the anti-Kell antibodies: IgG1 9/20, IgG1/IgG3 1/20, IgG1/IgG4 8/20, IgG1/IgG3/IgG4 2/20; and for anti-Duffy antibodies: IgG1 1/8, IgG1/IgG4 7/8. These results are partly at variance with previously published results.

The frequency of irregular blood group antibodies detected for the first time in pregnant women during the period 1975-80 has been examined. Whereas Rh(D)-negative gravidae in Norway are examined immuno-hematologically three times during pregnancy, Rh(D)-positive women are tested once only, usually early in pregnancy. Nevertheless, about one-third of the new cases of immunization within the Rh system were found in the Rh-positive women. In the latter, anti-E and anti-c were the Rh antibodies most frequently encountered. Among other irregular antibodies which can cause hemolytic disease of the newborn (HDN), those of the Kell and Duffy systems are the ones second in frequency and clinical significance to the Rh antibodies. In the present series about 40% of the new cases of immunization within the Rh, Kell and Duffy systems were found in Rh-positive women. This proportion would undoubtedly have been greater if also the Rh-positive women had been retested for the presence of irregular blood group antibodies towards the end of the gestation. Such a retesting of Rh-positive gravidae is desirable both for a better prediction and early diagnosis of HDN and to facilitate the procurement of compatible blood if the woman should need an emergency blood transfusion.

A "new' rare blood group antigen Rla (Rosenlund) is reported. The antigen is present in about 1 in 900 Norwegians. Nine unrelated Rl(a+) people were found. Studies of seven families, leading to the discovery of 20 additional Rl(a+) people, indicated the antigen is inherited as a Mendelian dominant character. Independent segregation was demonstrated between Rla and the ABO, MNSs, Rh, Lutheran, Duffy and Kidd blood group systems, the ABH secretor genes, and sex. The Rla antigen is inactivated by papain treatment. The corresponding antibody, anti-Rla, has so far been found in three sera that also contain antibodies to other rare blood group antigens.

A 'new', rare blood group antigen, Ola (Oldeide), is described. Only one Ol(a+) person was found among the 7,151 blood donors tested. Examination of the family of the proposita revealed 10 additional Ol(a+) persons. The study indicated that Ola is inherited as a Mendelian dominant character and segregates independently of the ABO, MNSs, P, Rh and Kidd blood group systems, of the ABH secretor genes, and of sex. Ol(a+) family members had depressed Rh antigens, while the Ol(a-) members had Rh antigens of normal strength. The depression was particularly pronounced for the C and E antigens, less marked for the D antigen. Individual antisera differed in their ability to demonstrate the presence of the antigens. Depression of the c and e antigens could not be demonstrated conclusively with the antisera available.

The rare blood group antigen previously referred to as the 'Haakestad antigen' is shown to be identical with the Hov antigen (numerical designation: 700.038). Family studies add AB0 and HLA to the systems already known to segregate independently from Hov. Among 2,021 Danish blood donors, 4 Hov+ persons were found. Anti-Hov activity has been demonstrated in several 'multiple-antibody sera'.