Although the expression patterns of the members of the tumour necrosis factor receptor and ligand families have extensively been studied by now-cytometry on stimulated peripheral blood mononuclear cells (PBMNC), little or no flow-cytometric or immunohistological data exist about their expression in lymphoid tissue. According to the data obtained from stimulated PBMNC, several members of these molecule families (e.g. CD40 ligand [CD40L], CD30, CD27, hOX40) have been considered to be either T-cell restricted or strongly T-cell associated. The present study on samples from palatine tonsils revealed that most of these molecules are also expressed by tonsillar B cells, The additional analysis of the co-expression of these molecules also disclosed the existence of CD40(+)/CD40L(+) and CD27(+)/CD70(+) (CD27L(+)) lymphoid cells in tonsillar tissue.