The nuclear localization of unoccupied oestrogen receptors has been demonstrated in MCF 7 (human breast tumour) cells by immunocytochemistry, and in GH3 (rat pituitary tumour) cells by enucleation techniques. The present study shows, by similar enucleation techniques, that high affinity (Type 1) aldosterone binding sites are similarly located in the nucleus of steroid-unexposed pituitary GH3 cells. It is, therefore, suggested that such high-affinity Type 1 sites, which are mineralocorticoid receptors in the kidney and glucocorticoid receptors in the hippocampus, are nuclear-associated proteins in the absence of steroid and are found in the cytosol compartment only upon cell disruption.