Evidence supporting the claim that specific phenothiazines, notably chlorpromazine and promethazine, may be used as sole agents for the treatment of cancer in man, has been reviewed. Selective destruction of cancerous tissue can be achieved by modulating energy metabolism in malignant cells. In the light of available information, the drug of choice is promethazine, the effects of which on the central nervous system are relatively weak. The maintenance of continuous pharmacological pressure against malignant growths forms an essential feature of the therapy. Protection against blood dyscrasias may be secured through the provision of adequate amounts of trace elements necessary for the function of enzyme systems which detoxicate active oxygen species. Tumour-cell death may be facilitated by nutritional supplements of specific polyunsaturated fatty acids. Interference from adventitious medications and drug resistance are discussed; appropriate therapy is outlined.