White adipose tissue is no longer viewed simply as a vehicle for lipid storage; instead, it is recognised as a major endocrine and secretory organ. White adipocytes release a number of lipid moieties, including fatty acids and prostaglandins. They also secrete a multiplicity of protein signals and factors, and these adipokines, which collectively constitute the 'adipokinome', have an extensive range of physiological actions. Foremost among the various adipokines is the cytokine-like hormone, leptin, which is synthesised predominantly in white fat. Leptin plays a critical role in the control of appetite and energy balance, with mutations in the genes encoding the hormone or its receptor leading to hyperphagia and profound obesity in both rodents and man. Leptin regulates appetite primarily through an interaction with hypothalamic neuroendocrine pathways, inhibiting orexigenic systems such as NPY and orexin A, and stimulating anorexigenic systems such as POMC. White fat also secretes several putative appetite-related adipokines, and these include IL-6 and adiponectin in particular, as well as IL-18. However, whether these factors are indeed significant signals in the regulation of food intake has not been established. Through leptin and the other adipokines it is now evident that white adipose tissue communicates extensively with other organs, including the brain, and plays a pervasive role in metabolic homeostasis.