Experimental approaches involving the perfusion of tissues and organs offer the advantage of improved physiological relevance over the use of isolated tissues or cells while at the same time being much more controlled and tissue-specific than studies in vivo. Nevertheless, there have been few metabolic studies performed in perfused white adipose tissue, largely because of the difficulty of the surgical technique involved. Although some methods have been described, they are difficult to use as perfusion protocols and their reproducibility is poor. We have modified a rat perfusion method, based on a modification of the Ho and Meng technique, for use with epididymal white adipose tissue (eWAT), and we present it here as a protocol to be reproduced. We also offer surgical solutions for the most common variants of vessel distributions in rats. Using the protocol described here, the perfused adipose tissue is viable and metabolically active, as indicated by the maintenance of tissue ATP levels and adiponectin secretion and by endogenous lipolysis regulation. Moreover, there is a high level of lipoprotein lipase activity in the endothelium of the tissue, which is heparin-releasable. Thus, this method is a useful and reproducible tool that allows the perfusion of eWAT for use in metabolic studies. Perfusion is a technique that faithfully reproduces the physiological environment in an isolated tissue. It allows the study of metabolic processes in physiological conditions because it involves the whole organ, maintaining its structure and cellular diversity. Moreover, substrates, hormones, drugs, etc., reach cells through physiological channels, the arteries and veins.In the early 20th century, the development of perfusion methodology in laboratory animals began in organs such as the heart and liver. Later, some studies were performed in perfused white fat tissue. However, this technique is more complicated than in other tissues. In 1963, Robert and Scow (1) published the first perfusion of rat parametrial white fat tissue, used in later studies (1-5). In 1964, Ho and Meng (6) described a perfusion technique for isolated rat epididymal white adipose tissue (eWAT), used as a reference for subsequent epididymal tissue studies (6-10). In all cases, the protocols described are very difficult to reproduce and use in metabolic studies.Alternatively, in humans, the use of microdialysis and arteriovenous techniques has been proposed to study white adipose tissue (WAT) metabolism (11). Although these methods are applicable to humans, they have several disadvantages, such as minimal control over the studied tissue and over the different factors released from the rest of the body.Based on the modification by Gubser, Di Francesco, and Bickel (7) of the Ho and Meng technique (6), we developed a detailed in situ perfusion method with the aim of providing an easily reproducible protocol useful for other researchers. This method is appropriate for use in metabolic studies involving the perfusion of different substances and collec...