Purpose: To present data suggesting that active immunization with lymphocyte immunotherapy is a treatment that has benefit in preventing miscarriage. Methods: Lymphocyte immunotherapy is given to women with a history of recurrent miscarriage or failure to achieve a successful pregnancy, despite several previous embryo transfers. Active immunization was combined with progesterone therapy. The lymphocytes were not refrigerated, but used fresh. Results: Compared to controls, i.e., progesterone therapy alone, the injection of paternal lymphocytes intradermally improved miscarriage rates and improved live delivered pregnancy rates per embryo transfer. Conclusions: The addition of progesterone treatment may act synergistically with lymphocyte immunotherapy, especially in primary aborters and tertiary aborters. However, it is important to use fresh – not refrigerated – stored lymphoctes.