This study was undertaken to examine the effect of parenteral nutrition upon body weight, tumor growth, plasma aminogram, tumor aminogram, nitrogen balance and histological change in rats with a transplanted tumor. Twenty-five male Donryu rats, having a subcutaneously transplanted Sato Lung Cancer were studied. They were divided into 5 groups. A silastic catheter was inserted into the superior vena cava via the left common jugular vein of rats of the infused group. Infusion continued for 7 days. Tumor size was three-dimensionally measured. All rats were sacrificed on the 8th day. The body weght increase in group I., Ⅱ., Ⅲ., Ⅳ and Ⅴ was 35.0g, 35.4g, -69.0g, 2.8g and -19.8g. The tumor growth rate in group I. Ⅱ. Ⅲ. Ⅳ and Ⅴ was 10.06, 4.15, 10.07, 8.01 and 4.75 respectively. Plasma aminogram showed markedly elevated levels of Thr in group Ⅳ, Ⅴ and Ser, Gly, Lvs, in group Ⅲ. On the contrary, lower levels of Val, Leu, Ile were found in group Ⅲ. ACNU had no effect on plasma aminogram. There was no difference between TPN and oral feeding as far as tumor aminogram was concerned. The nitrogen balance study in group Ⅲ revealed massive necrosis and small sized tumor cells. Tumor cells of group Ⅳ showed large multinclear cells and distinct chromatin. There was no significant difference between group Ⅱ and Ⅴ as far as anti-neoplastic effect of ACNU. Provision of adequate nutrition intravenously to tumor-bearing animals restores body weght and positive nitrogen balance. TPN has significant effect on intensive neoplastic therapy.