Over the last 16 years, 202 fetal tissue transplants have been performed in our department to treat 29 patients with severe inborn errors of metabolism without immunodeficiency, 26 patients with congenital and severe immunodeficiency diseases, and 2 patients with severe aplastic anaemia. The actuarial survival curve of patients with inborn errors of metabolism treated with fetal liver transplantation shows a 12-year survival of 77%. The condition of many of these patients has been improved by the treatment, but transplantation has had to be repeated in order to maintain clinical amelioration. Enzyme levels were not significantly and durably increased in peripheral blood but the quantities of substrates detected in sera and urines were significantly reduced and tissue deposits were stabilized.