There have been a number of recent developments in mechanisms of action of growth factors and their receptors with particular relevance to cancer. The tyrosine kinase receptor family, in particular, has been shown to be important in tumour growth. These receptors are the products of oncogenes, or can interact with other oncogene pathways. Thus, antibodies to either the receptor or its ligand can be used as therapeutic agents. Peptide analogues of ligands that can block receptor activation are also potential therapeutic agents.