The analysis of B-lymphocyte activation has been a tantalizing prospect for both immunologists and cell biologists, as B cells have the unique characteristics of possessing a well-characterized receptor and displaying a clear inducible response to a specific antigen. As outlined in this review, we now know much about the cellular events which occur when mature B cell encounters antigen within the peripheral lymphoid organ of an immunocompetent host. Our understanding of the molecular events associated with these cellular processes is currently limited, but such information will undoubtedly ensue. The greatest challenges remaining in B-cell immunology are immunoregulation and an understanding of how the enormous B-cell specificity repertoire is generated. These challenges require greater insight into lymphocyte triggering events and the early events in B-cell maturation. This review has not restricted itself to the phenomena associated with antigen-triggered mature splenic B cells, but has attempted to include aspects of B-cell development which are often overlooked or disregarded. In particular, attention has been drawn to certain nonspecific antigen-induced B-cell events, and to antigen-initiated developmental processes which precede mature B-cell development. Additionally, the commitment of triggered mature B cells to effector cell production has been reconsidered in light of current attempts to propagate normal lymphocytes continuously and in a manner which avoids terminal differentiation. The availability of such lines, together with increasingly refined technology, will hopefully allow us to resolve the remaining mysteries in B-cell development.