The transcriptional onset ofhGH-transgene in fish was studied in the following three cases: the first is inMThGH-transgenic F(4) common carp (Cyprinus carpio) embryos, the second is in nuclear-transferred embryos supported by the transgenic F(4) embryonic nuclei, and the third is in nuclear-transferred embryos supported by the transgenic F(4) tail-fin nuclei. RT-PCR results show that thehGH-transgene initiates its transcriptional activity from early-gastrula stage, the early blastula stage and even 16-cell stage in the first, second and third cases, respectively. It looks like that fish egg cytoplasm could just offer a very restricted reprogramming on transcriptional activity of specific gene in differentiated cell nuclei by nuclear transplantation.