A sheep type I interferon receptor (oIFNAR1) cDNA was isolated from a λ-ZAP library using a reverse transcription (RT)-PCR product probe generated from oestrous endometrial RNA. The oIFNAR1 cDNA was 79, 66 and 95% homologous to human, murine and bovine IFNAR1 cDNAs respectively. The encoded receptor was a 560-amino acid transmembrane protein 80, 66 and 95% similar to human, murine and bovine IFNAR1 respectively. Northern blot analysis of endometrial mRNA revealed the presence of 6·5, 4·3 and 3·7 kb transcripts. Using semi-quantitative RT-PCR the oIFNAR1 mRNA was not found to be down-regulated after 72 h treatment with bovine recombinant IFN-αI in in vitro experiments with endometrial explants.