Using synthetic peptide or recombinant protein as immunising antigens we have produced monoclonal antibodies and polyclonal antisera directed against targets of particular interest in leukaemia diagnosis. In this way we have prepared reagents which recognise all T or all B lymphocytes in routinely fixed paraffin sections which are unique in this respect. We have also produced monoclonal antibodies to molecules potentially involved in specific neoplastic transformations, implicated by virtue of the involvement of their genes in chromosomal defects in these neoplasms. In particular, we have produced antibodies recognising bcl-2, involved in follicular lymphoma, tal-1, involved in T-cell acute leukaemias and HRX involved in a variety of hematologic disorders. The application of these reagents to diagnosis has so far proved useful. In addition their use outside the field of leukaemia diagnosis has proved to be even more important in some cases.