Stimulation of tumour growth by intensive exogenous nutrient administration could be a major clinical problem when nutritional support is provided in malnourished cancer patients. Nutritional repletion has been clearly shown to stimulate tumour growth in animal models but not in humans. The purpose of this prospective study was to evaluate the effect of pre-operative nutritional support on the proliferative characteristics of gastric tumour cells evaluated by 3H-thymidine (3HT) incorporation and flow cytometry (FCM). Thirty-three malnourished patients with advanced gastric cancer were allocated randomly into two groups receiving different types of nutritional support during the interval between endoscopy and operation: parenteral and/or enteral hyperalimentation (Group 1), and oral alimentation as possible or peripheral fluids (Group 2). In 16 patients with diploid tumours the percentage of 3HT labelled cells and of cells in S+G(2)M phase did not differ between the multiple samples taken from the mucosal surface of the neoplasia. Tumour samples showed higher mean values of cycling cells than the surrounding normal tissue. Both methods (3HT - FCM) demonstrate that tumour cell proliferation is not enhanced following a prolonged period of pre-operative artificial nutrition.