Several native peptides can regulate tumour cell proliferation. After binding to specific membrane receptors they have the ability to stimulate or inhibit directly cell growth. Peptides can also control the regulation of endocrine or paracrine growth factor secretion. Agonist and antagonist molecules have been synthesized for therapeutic purposes. Hypothalamic neuropeptides are used in oncology. GnRH agonists lead to biochemical castration which is useful in treatment of hormone-dependent tumours (breast and prostate). Somatostatin analogues are beneficial in the treatment of gut neuroendocrine tumours and have demonstrated an antitumoural effect in experimental studies. Cytostatic agents, such as Gastrin Releasing Peptide antagonists, may be of interest as an adjuvant to chemotherapy or surgery in small cell lung cancer and other malignancies. The role of peptides in antigenic presentation, cell proliferation control and the metastatic process suggests a new therapeutic potential for these compounds. Progress in biotechnology could provide specific tools to screen new molecules and increase the understanding of mechanisms of action. Improvement in drug delivery techniques will allow for more convenient routes of administration.