We are trying to develop new drugs that will improve tumour killing in currently used imuno- and chemotherapy. The complement system is the body’s first line of defence against disease, able to kill invading bacteria and foreign cells. Cancer cells have on their surface protecting proteins, called regulators, which allow them to ‘hide’ from complement attack and survive. The factors that enable cancer cells to make large amounts of these regulators are not known but it is clear that if tumours could be prevented from making regulators then complement would much more efficiently kill the tumour. We propose to identify the factors controlling production of complement regulators and develop ways of reducing their production in tumours. We also suggest developing a new strategy for design of drugs that specifically activate on tumour surface and prevent production of the protective regulators. As a consequence, tumours will be more efficiently killed by complement that activates in imuno- and chemotherapy. The strategies will first be developed in cancer cells in the test-tube, the potential drugs then tested for therapeutic effect on human tumours in mouse animal model. Though here modelled in neuroblastoma, the strategy may be of much broader relevance to tumour therapy.