Porcine sperm heads were injected into mouse ovulated and in vitro matured oocytes. Both pronuclei were formed after injection into mouse ovulated oocytes. Additional labelling against 5-MeC and some histone modification revealed similarity to those changes that are typical for mouse zygotes. After porcine sperm head injection into in vitro matured mouse oocytes, no paternal pronuclei were formed. In the other part of the study, mouse sperm head were injected into mouse in vitro matured oocytes. The labelling against 5-MeC showed less extensive demethylation than is typical for ovulated oocytes. Our observation suggest that porcine sperm heads are capable of undergoing active demethylation in vivo matured mouse oocytes and that in vitro matured mouse oocytes posses lower sperm remodeling capabilities.