Embryo transfer in the pig is still very experimental but reduced generation intervals and accelerated genetic improvement could be achieved if younger gilts could be stimulated into an early puberty and used as donor animals. Stimulation of precocious puberty using a single dose injection of hCG and PMSG (PG600) has been shown to be successful (Schilling and Cerne, 1972). Pressing et al (1991) found that at 100 days gilts did not respond to pulsatile GnRH administration inferring that the pituitary-ovarian axis is not mature prior to this time. In this experiment exogenous gonadotrophins were administered to gilts between 100-180 days old in order to assess their ovarian response at both the stimulated heat and a second, natural heat.