Effects on fertility of female mice after hyper-immunization with human lactate dehydrogenase-C4 have been studied at (50 + 25 x 4) and (50 + 50 x 4) micrograms doses of protein for two consecutive cycles of pregnancy. Results of heterologous immunization are described in relation to the role of LDH-C4 in conception and contraception. (i) Low dose of Immunization produced higher antibody (Ab) titer as tested before mating followed by higher infertility (70%) than by a higher dose of immunogen (46%), taking pregnancy as the end point. (ii) However, the results were reversed after second mating. For example, low dose of immunogen produced insignificant infertility, whereas high dose of immunogen gave 80% infertility. Similar order was shown by humoral Ab titer before mating i.e., high infertility was associated with high Ab titer and viceversa. (iii) It shows that the LDH-C4 induced infertility is reversible as is evidenced by low dose of immunization. (iv) In contrary to infertile dams, immunized fertile dams delivered a significantly higher litter size as compared to non-immunized control dams. It is concluded that immunity due to LDH-C4 is beneficial for embryo survival suggesting an immuno-suppressive nature of LDH-C4. Nonetheless, infertility ensues when immune-suppression is overcome by its own immune-activation.