We studied the pattern of transcription of a human HLA-G transgene in mice using polymerase chain reaction (PCR) techniques. Transcription of the HLA-G transgene commenced in cells derived from embryos as soon as 48 hr after implantation of embryos in the uterine wall and continued for at least a further 48 hr during embryonic development. HLA-G transcripts were also present in RNA extracted from thymus, spleen and liver of adult HLA-G transgenic mice, although transcripts were not detected in RNA from any other tissues except testes of male transgenic mice. These results demonstrate that the restricted pattern of HLA-G transcription in embryo-derived trophoblast cells during the first trimester of human pregnancy is reproducible in mice. This suggests that transcription factors required for a highly regulated pattern of gene expression during embryonic development are present in murine trophoblast cells and provide a means to investigate the factors and study the consequences of HLA-G expression during development of the embryo.