Recently, it has been demonstrated that the immune function is preserved longer and spontaneous tumors occur less frequently in calorie-restricted (but not malnourished) mice. In the present report the effect of similar dietary manipulation on tumor growth, metastases, and survival was studied. C57BL/6 mice were fed regular laboratory diets, either restricted in calories or not restricted, and later inoculated with B16 melanoma sc, iv, or ip. Local tumor growth was found to be slower; however, survival after ip injection was no different, and the number of pulmonary metastatic colonies after iv injection was greater for the underfed mice. In this weakly immunogenic tumor model, factors in addition to immunity influenced tumor growth and were altered by calorie restriction.