In humans, adrenaline stimulates lipolysis, ketogenesis, thermogenesis and glycolysis and raises plasma glucose concentrations by stimulating both glycogenolysis and gluconeogenesis. The venous plasma adrenaline thresholds for these effects (410-680 pmol/l for the lipolytic and thermogenic effects and 550-1090 pmol/l for the glycemic, ketogenic and glycolytic effects) lie within the physiological venous plasma adrenaline concentration range of < 50 to approximately 1200 pmol/l under non-stressed conditions. Thus, adrenaline is undoubtedly frequently involved in the minute-to-minute regulation of these metabolic processes under conditions of daily living. In general, the extent to which the hormone is critically involved is unknown. Adrenaline is, however, known to play a secondary role in the physiology of glucose counter-regulation. Furthermore, individuals can survive in the absence of biologically active plasma adrenaline levels following bilateral adrenalectomy. Therefore, it seems likely that the hormone will be shown to play secondary roles in the regulation of lipolysis, ketogenesis and thermogenesis as well. It may well play more critical roles under stressful conditions and in pathophysiological states. Indeed, it has been shown to play a critical role in one pathophysiological state, the altered glucose counter-regulation in patients with established insulin-dependent diabetes mellitus.