BEIJING, May 30 -- A team of Shanghai scientists reported yesterday that it has performed the world's first successful transfer of human stem cells into goat embryos - taking an important step toward using genetic engineering to prevent disease.

    The research was published in the May 16 edition of the Proceedings of the National Academy of Sciences, a US scientific journal.

    "Our eventual purpose is to use stem cells to treat hereditary diseases," said Huang Shuzheng, a professor at Jiao Tong University's medical genetics institute and leader of the project.

    Over the past five years, Huang's team has transplanted stem cells taken from human umbilical cords into embryos carried by 50 goats.

    When the offspring were born, 39 were found to have some human genetic characteristics in their blood and internal organs.

    The research showed that stem cells, unspecialized cells that give rise to specialized cells, can be taken from one biological organism and transplanted into another without rejection, the scientists said.

    The 39 goats are now being raised on an experimental farm in Shanghai's suburban Songjiang District.

    Researchers eventually hope to use transplants of healthy human cells to treat hereditary diseases such as hemophilia. Injected into a developing embryo, normal stem cells could be used to "fix" a genetically linked disease, scientists believe.

    Previously, Huang said her team demonstrated that healthy stem cells can supplant liver-disease cells in embryonic mice.

    Huang and her fellow researchers admitted that developing a stem cell therapy to cure human diseases is still a long way off.

    The challenges are not only technological; there are ethical issues as well.

    Qiu Xiangxing, a professor of biological ethnics at the Chinese National Human Genome Center in Shanghai, said Huang's research so far is on safe grounds.

    But he also stressed that scientists should be extremely careful in carrying out genetic studies that mix material from animals and humans.

    "In China, it's not allowed to implant animal organs with human gene characteristics into human bodies," he said.

    "Nor can scientists use stem cells from human embryos that are more than 14 days old."

    He said Shanghai is now preparing to draw up a comprehensive code of ethics for biological scientists.