ABSTRACT Parthenogenetic mouse embryos were selected following in vitro activation, and transferred to the oviducts of pseudopregnant recipients. Decidua was evoked by 50–56 % of diploid parthenogenones compared to 35·1 % of haploid embryos with a single pronucleus, 37·5 % of immediate cleavage eggs and 77 % of fertilized eggs (controls). On day 4, 58·7 % of diploid parthenogenones were morphologically normal morulae or blastocysts; over 90 % of these ‘normal’ embryos evoked decidua when retransferred to recipients compared to 8·9 % of abnormal embryos flushed from the ‘transfer’ sides, suggesting that only ‘normal’ embryos could evoke decidua. Potentially diploid parthenogenones remained diploid on chromosomal examination on day 4.