Apolipoprotein A5 (ApoA5) is fast gaining attention as a key regulator of serum triglyceride concentrations. An ApoA5 mouse knock-out model produced an approximately four fold increase in serum triglycerides, whereas a knock-in model human ApoA5 produced 50–70% lower concentrations of mouse serum triglycerides. In, additions, peroxisome proliferators-activated receptor-agonists, which are used clinically to lower serum triglyceride concentrations, cause increased ApoA5 mRNA expression. Despite these compelling molecular biology data, relatively little is known about ApoA5 protein in human serum. Recently, it was demonstrated that ApoA5 is the present in the human serum detected by polyclonal antibodies against both the HN2 and COOH termini, although at much lower concentration than other apolipoproteins.