White adipose tissue was obtained from the mesentery, epididymis, omentum and subcutis of rats which were fed, fasted or fasted and then refed. Tissue samples were prepared using the glyoxylic acid method to detect adrenergic nerves by fluorescence histochemistry. Other tissue samples were fixed with an aldehyde solution containing sodium molybdate which is specific for catecholamine granules in nerve terminals. Thin and serial thick sections (0.25-0.5 micron) were viewed with a conventional electron microscope and with the high voltage electron microscope. With fluorescence microscopy it was found that most of the blood vessels except veins and venules were richly innervated. The most extensive branching of nerves down to the capillary level was found in the mesentery and epididymal fat of fasted-refed rats. Relatively few adipocytes appeared to be innervated. With electron microscopy, nerve terminals were found distributed with most blood vessels including capillaries, and with some adipocytes. Only 2-3% of all dipocytes were innervated by adrenergic nerves. It is suggested that in the adipose tissue sites studied the major adrenergic innervation is mainly for the supply of blood vessels.