From 643 sera of healthy women and men in 67 a positive reaction with B lymphocytes and/or monocytes of healthy subjects was found. Forty-seven sera gave only occasional weak reaction. Twenty sera were from 18 subjects (13 men without a transfusion in the case-history 5 women with pregnancy in the case-history). In nine sera of men (= 1.40%) HLA-A, B cytotoxins, usually bi-or multispecific, were detected, in four sera of men (= 0.62%) HLA-DR antibodies were present in two instances their specificity was assessed: anti-HLA-DR7, anti-HLA-DRI + weak DR4. All these antibodies can be considered natural. In three women HLA-A, B cytotoxins were detected, in two monocytic antibodies. From the results ensues that it is useful to test women donors with a case-history of pregnancy for the presence of HLA-antibodies. The author discusses whether antibodies revealed in sera of 13 men are really natural or whether they developed for other reasons.

Keywords: Antibodies /analysis/; Female; HLA Antigens /immunology/; HLA-A Antigens /immunology/; HLA-B Antigens /immunology/; HLA-DR Antigens /immunology/; Humans; Immunization; Male