The use of defibrotide and/or oligodeoxyribonucleotides having a molecular weight of 4000-10000 Dalton as an anti-tumour agent, alone or in combination with other active ingredients with anti-tumour action, is described. The oligotide may be produced by extraction from animal and/or vegetable tissues, in particular, from mammalian organs, or may be produced synthetically. The tumors which can be treated are preferably angiogenesis-dependent tumors, such as multiple myeloma or breast carcinoma.