Adjuvant parenteral nutrition of tumor patients receiving cytotoxic chemotherapy offers many potential advantages. There are some randomized studies with few cases looking at the effect of parenteral nutrition on tumor response and toxicity. In an own prospective randomized study on parenteral nutrition of colorectal cancer patients an increase of tumor response, prolongation of survival, or reduction of toxicity could not be achieved. Published controlled studies are discussed in a literature review. Parenteral nutrition of tumor patients receiving chemotherapy is not principally advantageous and should be restricted to special clinical situations.