Female mice of the AKR/J(AK) strain were fed a control diet (Purina chow) or a lipotrope-supplemented diet (Purina chow plus 2% D.L.-methionine and 1% choline chloride) beginning at one week after weaning. Mice of this inbred strain spontaneously develop thymic lymphoma, with close to 100% mortality expected by 12-13 months of age. Two separate experiments were carried out with 50 mice per group in one, and 40 mice per group in the other. The slopes of the survival curves for the animals in the control group and supplemented group of mice diverged after the animals reached 6.5 months of age. In both experiments, 20% of the mice receiving supplemented diet were still alive at one year, while 3% in one experiment and 8% in the other experiment survived in the control groups. Each experiment was terminated when the animals reached 13 months of age. At that time the survival rate of the controls was 2% and 4%, and survival in the groups of mice receiving supplemented diet was 14% and 18%. Necropsy revealed that the animals in both groups had advanced malginant lymphoma. The results demonstrate that intake of a chow diet that is supplemented with moderate quantities of methionine and choline results in enhanced survival of spontaneously leukemic AK mice, in comparison with animals of this strain fed the same diet without supplements of choline and methionine.