ABSTRACT: A paired sequential trial was undertaken to establish whether paternal mononuclear cells improved the prognosis in couples with recurrent abortions. For this purpose, 107-108 cells obtained from the blood of partners were injected intravenously, subcutaneously, and intra-dermally into women who had had three or more consecutive miscarriages with the same partner. Control women were given normal saline, injected in the same manner. The result of the sequential analysis showed that there was no significant beneficial effect of the cells compared to control. The overall success rate was 70% (32/46 couples). The success rate in patients given cells was 62% (13/21), while in those given saline it was 76% (19/25). While the overall success rate in this study compares with a number of other studies, we find an equally high success rate with non-immunized patients. We conclude that the value of immunization for the prevention of recurrent miscarriage has not been established.