This study aimed to confirm the presence of Blocking Factors (BFs) in Mixed Lymphocyte Culture (MLC) from female normal reproducer and sub-fertile rabbit inoculated with two injection of the allogenic lymphotherapy (LIT) to analyze its effect on rate fertility and pregnancy success. The BFs measuring was done intervening MLC with MTT-Formazan non-radioactive technique. It was demonstrated BFs presence in MLC in female rabbit groups.. In sub-fertile female reproducers treated with allogenic lymphotherapy a significant increase in the level of FBs after every LIT was observed, as well as a rate fertility increase.. Furthermore, it was established that BFs act on cell proliferation inhibiting the MLC of other species, clearly indicating that the inhibit effect of the BFs is inter-specific and no intraspecific as had sustain until now.This study aimed to confirm the presence of Blocking Factors (BFs) in Mixed Lymphocyte Culture (MLC) from female normal reproducer and sub-fertile rabbit inoculated with two injection of the allogenic lymphotherapy (LIT) to analyze its effect on rate fertility and pregnancy success. The BFs measuring was done intervening MLC with MTT-Formazan non-radioactive technique.It was demonstrated BFs presence in MLC in female rabbit groups.. In sub-fertile female reproducers treated with allogenic lymphotherapy a significant increase in the level of FBs after every LIT was observed, as well as a rate fertility increase.. Furthermore, it was established that BFs act on cell proliferation inhibiting the MLC of other species, clearly indicating that the inhibit effect of the BFs is inter-specific and no intraspecific as had sustain until now.