The expression of the cytokine and IFN-related genes was studied in mouse embryo using RT-PCR method capable of detecting low levels of mRNA. Total RNA was prepared from the days 7 embryos by acid guanidinium thiocyanate-phenol-chloroform (AGPC) method. cDNA was synthesized by M-MLV reverse transcriptase, and amplified using the specific oligonucleotide primers for IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, TNF-alpha, IFN-alpha, IFN-beta, IFN-gamma, IFN-alpha/beta receptor (IFN-alpha/beta R), IFN-gamma receptor (IFN-gamma R), interferon reguratory factor (IRF)-1, IRF-2 and 2'-5' oligoadenylate synthetase (2-5AS) by PCR method. Although the expressions of IL-1 beta, IL-4, IL-5, IL-6, TNF-alpha and IFN-gamma mRNA were detected in all the embryos tested, the expressions of IL-2, IL-3, IFN-alpha and IFN-beta mRNA were not detected at all. On the other hand, the expressions of IFN-related genes such as IFN-alpha/beta R, IFN-gamma R, IRF-1, IRF-2 and 2-5AS mRNA, were also detected. These results suggest that these cytokine may play an important role in early embryonic development.