ARP4 is a fasting-induced adipose factor. It was identified as an adipocytokine up-regulated by fasting, by peroxisome proliferator-activated receptor agonists, and by hypoxia. At the protein level, in human and mouse blood plasma, ARP4 was found to be present both as a native protein and in a truncated form. Differentiation of mouse 3T3-L1 adipocytes was associated with the production of truncated ARP4, whereas in human white adipose tissue and SGBS adipocytes, only the native ARP4 could be detected. Interestingly, the truncated ARP4 was produced by human liver. Experimental data suggest that ARP4 is mainly presented in human blood plasma in a truncated form (ARP4-S2), whose level is increased by fenofibrate treatment. Levels of both truncated and native ARP4 showed marked inter individual variation but were not associated with body mass index and were not influenced by prolonged semistarvation.