Previous reports have suggested that the conversion of nor-adrenaline to adrenaline is dependent on very high plasma levels of glucosteroids. It has been postulated that this is achieved because the very high level of glucosteroid in the adrenal cortical venous effluent preferentially perfuses the phaeochromocytes before entering the main adrenal vein. No evidence for this portal circulation has been found. It has now been demonstrated that the venous drainage from the phaeochromocytes enters the large venous trunks emerging from the adrenal cortex and not the reverse. The adrenal gland is a composite gland made up by the incorporation by the adrenal cortex of chromaffin tissue during foetal life at a stage when the primitive vasculature of the cortex has already been laid down. The current data suggest that there are two circulations in the adrenal gland, one cortical and the other medullary, and that although the two become closely interlinked during foetal life, some independence remains in adult life. The cortical circulation consists of the cortical arteries and their veins which drain into large trunks at the corticomedullary interface and then directly via larger trunks into the central vein. The medullary circulation consists of the medullary arteries of Flint and their venae comites enclosed in a capsular sheath and an alternative venous exit via the delicate, spidery sinusoids which enter the radicles of the central vein. There is a limited alternative route for cortical blood via the venae comites of the medullary arteries.