Apolipoprotein CIII (apoCIII), a major constituent of triglyceride-rich lipoprotein, has been proposed as a key contributor to hypertriglyceridemia on the basis of its inhibitory effects on lipoprotein lipase. Many immuno-chemical methods have been developed for human apoCIII quantification, including ELISA. However, a sensitive and quantitative assay for nonhuman primates is not commercially available. We developed a sensitive, quantitative, and highly specific sandwich ELISA to measure apoCIII in both nonhuman primate and human serum. Our assay generates a linear calibration curve from 0.01 mu g/ml to 10 mu g/ml using an apoCIII standard that was purified from cynomolgus monkey serum. It is highly reproducible (intra-and interplate CV < 5% and < 8%, respectively), sensitive enough to distinguish 10% difference of apoCIII present in serum, and has no interference from purified human apolipoprotein AI, AII, B, CI, CII, or E. The same assay can also be used to measure human apoCIII with a linear calibration curve from 0.005 mu g/ml to 1 mu g/ml using purified human apoCIII as the standard. This fast and highly sensitive ELISA could be a useful tool to investigate the role of apoCIII in lipoprotein transport and cardiovascular disease.-Wang, Y., Z. Song, J. D. Wagner, C. Pachuk, and R. R. Subramanian. Development of a sensitive ELISA to quantify apolipoprotein CIII in nonhuman primate serum. J. Lipid Res. 2011. 52: 1265-1271.