Human adipose tissue is a major site of expression of inhibin beta B (INHBB) which homodimerizes to form the novel adipokine activin B. Our aim was to determine if molecules needed for a local action of activin B are expressed in adipose tissue. Microarray analysis showed that adipose tissue expressed activin type I and If receptors and that the expression of activin receptor-like kinase 7 (ALK7) was adipose tissue specific. In obesity discordant siblings from the SOS Sib Pair Study, adipose tissue ALK7 expression was higher in lean (n = 90) compared to obese (n = 90) subjects (p = 4 x 10(-31)). Adipose tissue ALK7 expression correlated with several measures of body fat, carbohydrate metabolism and lipids. In addition, ALK7 and INHBB expression correlated but only in lean subjects and ill Subjects with normal glucose tolerance. We conclude that activin B may have local effects in adipose tissue and thereby influence obesity and its comorbidities. (C) 2009 Elsevier Inc. All rights reserved.