Human plasma contains two lipid transfer proteins involved in the remodelling of plasma lipoproteins; cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP). CETP mediates the transfer/exchange of cholesterylesters, triglycerides and phospholipids between high-density lipoproteins (HDL) and chylomicron (remnants), very low-density lipoproteins (VLDL) and low density lipoproteins (LDL). The physiological function of PLTP is unknown. It is able to transfer phospholipids (but not neutral lipids) between lipoproteins and to modulate HDL particle size in vitro. The effects of acute endogenous hyperinsulinaemia on plasma CETP and PLTP activity, as well as on lipid and lipoprotein levels, were assessed in eight healthy men during a 3-h hyperglycaemic clamp. Another group of seven men received an infusion of an equal volume of saline in order to detect possible dilution effects or effects on lipoprotein changes over time (control group). Plasma cholesterol and triglyceride concentrations fell during the clamp and the decreases were significantly different from the minor changes during saline infusion in the control group (p < 0.05 and p < 0.01, respectively). Plasma CETP activity levels did not change, but plasma PLTP activity levels decreased by 7.7 and 5.1% after 2 and 3 h of hyperglycaemia (p < 0.01 for each time-point). The hyperglycaemia-induced mean percentage change in PLTP activity levels during the 3 h of the clamp was greater than the essentially absent change during the NaCl infusion (p < 0.05). Plasma PLTP activity during the clamp was related negatively to the insulin sensitivity index (p < 0.01 by analysis of covariance). It is concluded that acute hyperglycaemia-induced hyperinsulinaemia lowers plasma PLTP, but not CETP activity levels, either directly or in conjunction with an effect on plasma lipoproteins.