aOFM (Figure 4) allows continuous on-line monitoring of metabolic processes in the subcutaneous adipose tissue, e.g. glucose and lactate, as well as larger analytes such as insulin (5.9 kDa). The role of polypeptides for metabolic signaling (leptin, cytokine IL-6, TNFα) has also been studied with aOFM. aOFM allows the quantification of proteins (e.g. albumin size: 68 kDa) in adipose tissue and thus opens up the possibility to investigate protein-bound drugs directly in peripheral target tissues, such as highly protein-bound insulin analogues designed for a prolonged, retarded insulin action. Most recently, aOFM has been used to sample agonists to study obesity, lipid metabolism and immune-inflammation. Applications of aOFM include ex vivo studies with tissue explants and preclinical and clinical in vivo studies.