In some mAbs combination, we cannot rule out a simple additive effect due to the involvement of two mAbs reacting with independent antigens expressed by the tumour cells, but in the case of the coinjection of anti-HLA-DR and anti-CD5, or anti-CD71 and anti-CD5 mAbs, the clear advantage of same amounts of mixed mAbs over single mAb, as demonstrated in the i.p. model, are definitely in favour of a synergistic anti-tumour effect. The gene discussed is CD5; the disease is neoplasm.