Recent evidence suggests that immunological factors could play a role in the aetiology of habitual abortion. In this study, 71 couples with habitual abortion (i.e. more than 3 successive abortions) were investigated. Sharing of HLA-A, B, DR between partners was not found to be significantly increased. Anti-HLA antibodies in women against their partners' lymphocytes were found in 18.3%. After immunization with 10(7)-10(8) lymphocytes obtained from husband or unrelated donor, there was a seroconversion rate of 61% in those without antibodies initially. This was not dependent on the number of cells injected, source of cells, degree of sharing of HLA antigens or whether the couple were primary aborters (i.e. having had no advanced pregnancy), or secondary aborters. Seven pregnancies have resulted following the immunization procedure so far, 5 occurring in cross-match positive patients and 2 in cross-match negative. Growth retarded infants resulted from the pregnancy of 1 primary aborter and 2 secondary aborters.