ProblemIntrauterine administration of autologous peripheral blood mononuclear cells (PBMCs) activated by HCG in vitro was reported to improve implantation rates in patients with repeated failure of IVF-ET (in vitro fertilization-embryo transfer). In this article, the value of intrauterine administration of PBMCs before embryo transfer and its optimal cell culture method will be investigated. Method of studyPatients who had not experienced successful pregnancy despite three or more IVF-ET sessions were enrolled in this study (n=240, 240 cycles). PBMCs were obtained from patients themselves and were cultured with HCG for 24hours. Twenty-four hours later, PBMCs were then administered to the intrauterine cavity of that patient from the study group (n=93, 93 cycles). The control group (n=105, 105 cycles) underwent ET without intrauterine administration. ResultsClinical pregnancy rate, implantation rate, and miscarriage rate in the PBMC-treated group (46.24% and 23.66%, n=43 and 22, respectively) were significantly higher than those in the non-treated group (20.95% and 11.43%, P<.05; n=22 and 12, respectively). ConclusionThese findings indicate that intrauterine administration of autologous PBMC activated by HCG in vitro effectively improves embryo implantation in patients with three or more IVF failures.