The objective of this study was to determine whether porcine PAG (poPAG) genes are expressed in embryos as they develop from the 1-cell stage to expanded blastocysts, and whether expression differed according to how embryos had been derived. Embryos at various preimplantation stages were assayed after in vivo fertilisation, after in vitro fertilisation of in vitro-matured oocytes, or following parthenogenetic activation of in vitro-matured oocytes. The presence of PAG transcripts was determined at the1-, 2-, and 4-cell, compact morula and blastocyst stages by reverse transcription-PCR procedures with PAG 1- and PAG 2-specific primers, followed by Southern blotting. The mRNAs for poPAG 1 and 2 were detected in in vitro-derived, in vivo-derived and parthenogenetically derived blastocyst stage embryos. In some replications poPAG 1 could be detected as early as the compact morula stage and poPAG 2 could be detected as early as the 4-cell stage. Our study revealed that poPAG 1 and 2 genes are expressed as early as the compact morula stage and 4-cell stage, respectively, in normal embryos and in parthenogenetically derived blastocysts. Thus it appears that the poPAGs are not maternally imprinted and they may be useful as potential candidates for markers of developmental competence.