Adipose tissue is a type of connective tissue whose extracellular matrix (ECM) components are poorly characterized in vivo. Several in vitro studies have suggested a regulatory role for the ECM molecules during adipocyte differentiation. Since no data are available concerning the in vivo expression of the main ECM components such as fibronectin, collagen IV, laminin and heparan sulfate proteoglycan in the adipose tissue, we investigated the presence of these molecules by immunohistochemistry. We show that fibronectin isoforms are not expressed in fully differentiated subcutaneous adipocytes whereas collagen IV, laminin and heparan sulfate are detectable around single adipocytes, ie in the region corresponding to the basement membrane. These data are supported by previous in vitro studies showing a strong decrease of fibronectin synthesis during adipocyte development whereas basement membrane molecules seem to increase during adipocyte differentiation.