Many questions were raised during this multidisciplinary meeting during which geneticists, haematologists, embryologists, immunologists, transplant surgeons and physicians exchanged views on these questions. The second part of the meeting was devoted to an examination of the mechanisms of medullary deficiency. A more clinical approach was taken to the epidemiological, molecular and genetic aspects of medullary deficiency. There was also discussion of various therapeutic methods, including transplants, the use of haematopoietic growth factors, immunosuppressive treatments and gene therapy. Proceedings of the joint international workshop on "Foetal and neonatal hematopoiesis and mechanisms of bone marrow failure", Paris, April 1995.