Monoclonal antibodies have become an important treatment modality in cancer therapy. Genetically engineered chimaeric and humanised antibodies have demonstrated activity against a variety of tumours. Whereas the humanised anti-CD33 monoclonal antibody HuM195 has only modest activity against overt acute myeloid leukaemia (AML), it can eliminate minimal residual disease detectable by reverse transcription-polymerase chain reaction in acute promyelocytic leukaemia. High-dose radioimmunotherapy with beta-particle-emitting isotopes targeting CD33, CD45 and CD66 can potentially allow intensification of antileukaemic therapy before bone marrow transplantation. Conversely, alpha-particle immunotherapy with isotopes such as bismuth-213 or actinium-225 offers the possibility of selective tumour cell kill while sparing surrounding normal cells. Targeted chemotherapy with the anti-CD33-calicheamicin construct gemtuzumab ozogamicin has produced remissions as a single agent in patients with relapsed AML and appears promising when used in combination with standard chemotherapy in the treatment of newly diagnosed AML.