In 1868, Ernst Neumann recognized that blood cells re quire continuous replenishment during postnata1life. Before him, the assumption was that cells of the blood, like nerves once formed in the embryo, remain in the body throughout life. Neumann also recognized that this process occurred within the bone marrow, because this tissue provided a fa vorable environment for proliferation and differentiation of blood cell precursors. Vera Danchakoff, the Russian embryologist working in the US, in 1916 made an analogy to the soil and the seed. Bone marrow forms the soil, providing a favorable environment for the growth of seed, the hemopoietic stem cell, and other progenitor cells. Imagine in the remote past a heap of similar tree seeds. These seeds develop in our moderate climate into a tall and many branched tree. Suppose the wind bears a part of the seeds away and brings them to a land possessing different environmental conditions, we will say the arc tic lands. There the seeds may develop but they may pro duce trees no higher than our moss."

In 1868, Ernst Neumann recognized that blood cells re quire continuous replenishment during postnata1life. Before him, the assumption was that cells of the blood, like nerves once formed in the embryo, remain in the body throughout life. Neumann also recognized that this process occurred within the bone marrow, because this tissue provided a fa vorable environment for proliferation and differentiation of blood cell precursors. Vera Danchakoff, the Russian embryologist working in the US, in 1916 made an analogy to the soil and the seed. Bone marrow forms the soil, providing a favorable environment for the growth of seed, the hemopoietic stem cell, and other progenitor cells. Imagine in the remote past a heap of similar tree seeds. These seeds develop in our moderate climate into a tall and many branched tree. Suppose the wind bears a part of the seeds away and brings them to a land possessing different environmental conditions, we will say the arc tic lands. There the seeds may develop but they may pro duce trees no higher than our moss."

Perhaps no scientific field in recent years has gained in techniques and applications as much as molecular biology, and it is certainly no ex aggeration to.say that among all the applications of molecular biology, hematology in general, and hemopoiesis in particular, have benefited most. Owing to the applications of molecular biology, we now live in a golden era of hemopoiesis. Our understanding of the intricate regulatory system in hemopoiesis has vastly expanded. The potential for future exploration is ever expanding, and finally, the possibility of gene manipulation, has provided the promise of fundamental treatment and "cure" of many genetic disorders involving hemopoietic cells. In the ambiance of this rapidly moving scientific era, the necessity for review of what is being accomplished and where the technical potential is taking us needs no argument. This volume presents the proceedings of the third annual symposium on the Molecular Biology of Hemopoiesis, held in the Rye Town Hilton, New York, November 6 and 7, 1987, under the auspices of New York Medical College, Valhalla, New York. The fact that this was the third regular symposium covering this area in itself testifies to a need for exchange of the rapidly developing knowledge in this area. But this third symposium also coincided with the centennial of the National Institutes of Health and consequently the symposium was dedicated to this festive occasion."