Experimental models using immunization with known haptens have shown that germinal centres develop from only a limited number of precursor cells which expand in an oligoclonal fashion. Using a panel of antibodies raised against the idiotype of follicle centre cell lymphomas and known to be reactive only with a few normal B cells, we could demonstrate that individual clones can be identified within germinal centres of individual follicles of human lymph nodes and tonsils. Therefore also in humans in a non-experimental, natural situation, germinal centres expand in an oligoclonal fashion.