We have studied the accretion of lipids in growing mice. We measured the rates of synthesis and degradation of triglycerides in epididymal fat pads of mice maintained for 44 days on a low-fat, high-carbohydrate diet (I) or a high-fat, lowcarbohydrate diet (II). ²H₂O was added to the drinking water for 14 days. Rates of incorporation/washout of ²H to/from C1 of triglyceride-glycerol showed that triglyceride synthesis was greater than triglyceride degradation (net triglyceride balance was ∼2.5 times greater in II than in I). The data also show that the contribution of de novo lipogenesis to triglyceride-bound palmitate was ∼3 times greater in I than in II. This was consistent with a greater relative intake of carbohydrate in I vs. II. The rates of incorporation and washout of newly synthesized (²H-labeled) palmitate into and from triglycerides were also measured. Those data suggested a remodeling of triglyceride-bound fatty acids. On measuring the profile of triglyceride-bound fatty acids, we observed a decrease in the relative abundance of triglyceride-bound palmitate and stearate and an increase in triglyceride-bound oleate and linoleate. This was observed in I and II. In summary, diet substantially affects the deposition and modeling of triglycerides in adipose tissue during growth. ²H₂O can be used to examine the mechanisms responsible for the accumulation of triglycerides, e.g., factors that affect 1) triglyceride synthesis and degradation and 2) the source of fatty acids that are used in esterification.