Relaxin, a member of the insulin superfamily, has diverse functions in both reproductive and nonreproductive tissues. The aim of the present study was to evaluate the effects of recombinant relaxin on the in vitro maturation of porcine oocytes and their subsequent embryonic development following in vitro fertilization. Three concentrations of relaxin (1, 10, and 100 ng/ml) were used in the in vitro maturation (IVM) medium [TCM supplemented with 10% (v/v) porcine follicular fluid, 10 ng/ml of epidermal growth factor, 4 IU/ml of pregnant mare serum gonadotropin, and (only for the first 22 hr) 4 IU/ml of human chorionic gonadotropin]. Relaxin was used during the entire IVM period. Nuclear maturation of oocytes was examined under ultraviolet light following staining with bisbenzimide (Hoechst 33342) for 5 min and mounted on a glass slide. The glutathione (GSH) content in oocytes, an important indicator of cytoplasmic maturity, was measured using a micro-glutathione assay. Cryopreserved boar semen was used for in vitro fertilization. Embryos were cultured in modified NCSU-23 medium supplemented with 0.5 mM pyruvate and 5 mM lactate. Although nuclear maturation of oocytes did not vary, the GSH content in oocytes was significantly higher when cultured with 1 ng/ml (7.9 pmol/oocyte) and 10 ng/ml (8.47 pmol/oocyte) compared to a control group. However, no additional beneficial effect was observed when 100 ng/ml of relaxin was added to the IVM medium. A significantly higher rate of blastocyst formation was observed with 10 ng of relaxin (32.4%) compared to the control (14.4%) or 100 ng of relaxin (21.4%). No difference between 1 ng and 10 ng was observed in terms of the blastocyst production rate. The inner cell mass cell numbers in relaxin-treated groups were significantly higher than control, and trophectoderm cell number was the highest in the 10 ng relaxin group. Relaxin (10 ng/ml) can be supplemented in IVM medium to support the maturation of porcine oocytes.