AbstractAdult rats fed a low‐fat diet or diets containing 15% of either tripalmitin, triolein or trilinolein were injected intraperitoneally with H3‐labeled acetate. Those which received fat were also given by mouth, simultaneously with acetate, the 1‐C14‐labeled sodium salt of the respective dietary fatty acid. The fate of the tagged material was followed by time‐spaced biopsies of subcutaneous adipose tissue and by collection of the expired C14O2.After 72 hr, 51, 64, and 52% of the dietary palmitate, oleate, and linoleate, respectively, were catabolized, as indicated by the corresponding percentages of the label having been excreted as C14O2. Dietary linoleate was relatively less incorporated into body triglycerides than palmitate and oleate. Animals ingesting diets of 15% triolein had only about one‐half the amount of phospholipids in their tissues as had the other groups.The distribution of both the C14 and H3 labels in the tissue triglycerides showed that all diets containing fats decreased fatty acid synthesis but did not inhibit conversion of palmitate to oleate. Conversions of oleate or linoleate appeared to be through acetate. As a result of these factors, the fatty acid composition of the tissue triglycerides after 3 months舗 ingestion of tripalmitin was essentially the same as that of the low‐fat group, whereas the ingestion of triolein produced triglycerides with a very high content of oleic acid. Trilinolein ingestion produced effects similar to triolein but to a less pronounced degree.Both the respiratory C14O2 and the C14‐ and H3‐labeled fatty acids in subcutaneous adipose tissue exhibited a second rise in specific activity 12 to 24 hours after the administration of the label.