The study of anti-HL-A immunization was carried out on 26 sera taken from multiparous women who had had at least 4 pregnancies and who had never been transfused. In 20 of these cases, it was possible to define the HL-A phenotype of the husband and wife. As many well-defined sera were detected in multiparous women as in primiparous women. However, persistence of antibodies from one pregnancy to another can make the sera of the multiparous women more polyspecific than the sera of the primiparous women. One cross-reaction was described between the W14, HL-A5 and W5 antigens, and the cross-reaction between the HL-A7 and HL-A8 antigens was confirmed.