Nutritional support in chemotherapy and radiation therapy patients is a very attractive concept. This group of patients frequently begins treatment malnourished, and the malnutrition becomes worse because of treatment-related nausea and vomiting, mucositis, fever and other side effects. Effective nutritional support would enhance wound healing and visceral function, improve cellular immunity and allow delivery of adequate drug and irradiation doses, thereby increasing response rates and prolonging survival. Unfortunately, standard techniques of parenteral nutritional support have had only limited success in advanced cancer patients. Weight gain is possible and immune function may be improved, but definite benefit in response rates and survival with chemotherapy and radiation remains to be proven. Currently the author believes that the following are acceptable indications for parenteral nutrition in chemotherapy and radiation patients: patients who cannot eat or digest properly because of tumor obstruction, surgical resection of gut, or other complications who have a reasonable life expectancy; cachectic patients with responsive neoplasms who could not tolerate aggressive treatment without short-term nutritional support; and patients suitable for trials of nutritionally modified solution or alterations in standard techniques. Future studies might consider longer periods of support, increased concentrations of nutrients or, conversely, decreased amounts of nutrients needed by the tumor, if such needs could be identified.