The study was designed to compare, in a homogeneous, normolipidemic population, the postprandial responses of plasma lipids, in particular, high-density lipoprotein (HDL) constituents, after administration of a polyunsaturated fat and a more saturated fat.Emulsions of 100 g corn oil (CO) and 100 g beef tallow (BT) were given in a crossover protocol to 12 male subjects (21-24 years). Plasma cholesterol (TC), triglycerides (TG), and HDL lipid and protein constituents were measured at 0, 2, 4, 7 and 10 hours.A postprandial increase in TG at 2 hours after CO ingestion (96%) was twice that with BT (48%); TG returned to near fasting levels at 10 hours after ingestion of either fat. Areas under the TG response curves for CO and BT were 6.29 +/−1.67 and 1.75 +/−0.60 mmol×hour/L (mean +/−SE), respectively. TC and low-density lipoprotein cholesterol (LDL-C) levels were unchanged at 10 hours after CO ingestion, but they were increased 8.1% and 9.3%, respectively, with BT. Both fats increased HDL TG at 2-4 hours, and both similarly increased HDL free cholesterol, cholesterol ester, phospholipid, apolipoproteins A-I and A-II, and lipoprotein (A-I) levels at 7-10 hours. Changes in HDL were predominantly in HDL3.The increase in LDL-C with BT at 10 hours suggests that levels may be abnormally elevated in“fasting”samples, dependent on the amount and type of fat in a prior meal. The increase in LDL-C is consistent with short-term regulation of hepatic LDL-receptor activity and/or LDL synthesis. Similar increases in HDL constituents at 7-10 hours after CO or BT, despite the difference in TG responses, suggests differences in the metabolism of chylomicrons and/or HDL due to the type of fat ingested.