It has been demonstrated that the Xenopus oocyte can translate rabbit haemoglobin messenger RNA (mRNA) following microinjection of the message into the cell. The Xenopus oocyte has since been shown to be capable of translating a variety of messenger RNAs from different species. This system has proved useful in un-erstanding the mechanism of message translation and has also provided information about the translation capability of the Xenopus oocyte. Several other cell types, including HeLa cells and fibroblasts, can also translate exogenous message injected into the cell. However, there have been no reports of injection of mRNA into oocytes or fertilised one-cell ova of mammalian species. Nevertheless, the latter system could be of considerable use in studying the processing of exogenous messages in a mammalian system undergoing development, as well as providing insight into the way the early embryo processes injected messages and the protein products of such messages. We report here the results of injecting message into the fertilised one-cell mouse ovum and show that both mouse and rabbit globin mRNA are translated in this system.