GERMINAL centres are dynamic microenvironments of B-lympho-cyte differentiation, which develop in secondary lymphoid tissues during immune responses^1-3. Within germinal centres, activated B lymphocytes proliferate and point mutations are rapidly introduced into the genes encoding their immunoglobulin receptors^4-10. As a result, new specificities of B cells are created, including those with a heightened capacity to bind the immunizing antigen^4-11. Immunoglobulin gene mutation can also lead to reactivity to self antigens^12-14. It has been suggested that any newly formed self-reactive B cells are eliminated within the germinal centre in order to avoid autoimmunity^15,16. Here we present evidence that antigen-specific, high-affinity, germinal-centre B cells are rapidly killed by apoptosis in situ when they encounter soluble antigen. The effect seems to act directly on the B cells, rather than through helper T cells. Furthermore, the apoptosis is unique to germinal-centre cells, and is only incompletely impeded by constitutive expression of the proto-oncogene bcl-2. This phenomenon may reflect clonal deletion of self-reactive B cells within germinal centres.