Hybridomas which secrete monoclonal antibodies (MAbs) reacting with doxorubicin (DXR), a widely used anthracycline cytotoxic antibiotic, have been obtained by fusing NSO/P3 mouse myeloma cells with spleen cells from BALB/c mice immunized with DXR-BSA conjugate. The best producer among the several clones obtained was expanded and the secreted MAb (MAD2) purified and characterized. MAD2 cross-reacts to varying degrees with anthracycline compounds such as some DXR analogues and derivatives, but does not recognize anthracene and anthraquinone structures, with the exception of weakly reacting Mitoxantrone. MAD2 and the panel of MAbs which are at present being purified may become a tool for studying the relevance of different domains of the anthracyclin molecule in terms of biologic activity.