Functional immunoglobulin gene rearrangement is a sine qua non for successful B cell development in mammalian bone marrow, but other factors are also important. Studies reported during the past year have contributed new insight into the surface receptor complexes and signaling outcomes that influence the fate of B cell precursors. Identification and characterization of secreted and membrane-associated stromal cell products, and their actions on B-cell precursors, was a parallel area of ongoing investigation.