The value of nutritional support during cancer therapy continues to be debated. Data from studies concerned with nutritional rehabilitation of malnourished cancer patients suggest that in certain patient subgroups, total parenteral nutrition may improve tolerance to and increase efficacy of anti-neoplastic treatment modalities. In contrast, other investigators have questioned whether nutritional support of cancer patients may actually benefit the tumor at the expense of the host. Animal tumor model studies indicate that further research is warranted to ascertain whether human host and tumor tissue differentially utilize nutrient substrates and whether these differences may be used to the advantage of the host.