Cholesteryl ester transfer (CET), plasma, lipoprotein lipid and phospholipid composition were studied in insulin-treated baboons with chronic streptozotocin-induced diabetes. In these diabetic animals, CET measured both as the mass (p < 0.001) and isotopic transfer (p < 0.05) of CE from HDL to the apo B-containing lipoproteins (VLDL+LDL) were significantly accelerated compared to controls and the response closely resembled that recently reported in diabetic humans. No significant differences were present in plasma triglyceride, cholesterol, or HDL-C or in lipoprotein core or surface lipid composition. Thus, despite the fact that they did not display the same spectrum of abnormalities in lipoprotein composition, these insulin-treated diabetic baboons demonstrated an abnormality in CET identical to that described in humans. These findings suggest that this non-human primate may provide a suitable diabetic animal model in which to better characterize the mechanisms that underlie this potentially atherogenic disturbance in lipoprotein transport.