Although the isolation and characterization of functionally distinct B-cell subsets has been a major preoccupation of immunologists for the past two decades, only recently has it been recognized that the various B-cell subsets may be disparately selected during their development and maturation on the basis of their expressed Ig V regions. Thus, pre-B cells are selected for clonal expansion and maturation by virtue of the amino-acid sequence of their nascent H chains and newly emerging B cells may be selected for longevity and subset distribution on the basis of both clonotype-specific and relatively non-specific interactions of their surface Ig receptors.