A prospective study was carried out on 153 couples with recurrent abortions who desired pregnancy. The object was to determine the incidence of raised luteinizing hormone (LH) levels; to compare the outcome of further pregnancies in habitually aborting women with and without raised circulating LH concentrations; and to assess whether the efficacy of paternal leukocyte immunization is affected in the presence of raised LH concentrations. Of the 153 women with recurrent abortions (> 3) included in this study, 56 (36.6%) had follicular phase serum LH concentrations > 10 mIU/ml. Of the 103 pregnancies that were followed prospectively, 65 (63.1%) resulted in a birth of a live infant. There was no significant relationship between the pregnancy outcome and LH concentrations. Women who underwent immunization with paternal leukocytes had significantly more live births (75.8%) than those who were not immunized (43.6%). However, the live birth rate was lower after paternal leukocyte immunization in the presence of raised LH concentrations or a raised LH/follicle stimulating hormone (FSH) ratio.