Monoclonal antibodies have progressed from the laboratory to the clinic. Although recognised in diagnosis there are still problems as far as their therapeutic use is concerned. This review looks at the history, principles of active specific immunotherapy, clinical experience with monoclonal antibodies in therapy of solid tumours, in particular the development of new bispecific monoclonal antibodies, and trials in ovarian, breast and colorectal cancer. Immunoconjugates, linked with radionuclides and cytotoxic drugs, indicate future developments. Conditions for successful therapy, especially with adjuvants in patients with small tumour residues, are also described.