Oral feeding of mice with hypercaloric diets inhibited growth of a hyperdiploid Ehrlich ascites tumor significantly and modified proliferation kinetics of tumor cells if feeding started 7 days before tumor transplantation. Furthermore, the tumor take rate was significantly reduced. The 4 hypercaloric diets contained as main energy sources carbohydrates, or unsaturated fatty acids, or saturated fatty acids, or a mixture of these substrates. Inhibition of tumor growth was not observed if hypercaloric feeding started on the same day the tumor transplantation occurred. Tumor bearing animals lived significantly longer compared to controls if they are on a hypercaloric diet with unsaturated fatty acids as main energy source. Survival was not influenced by the time feeding started. That means that partial prevention of cachexia was the main reason for longer survival. Feeding with a diet poor in proteins led in both experimental sets to a statistically not significant shortening of the median survival time compared to controls.