Increased circulating levels of melanocyte-stimulating hormone (MSH) have been found in patients who had undergone adrenalectomy for Cushing's disease and in patients with Addison's disease; these increased levels were suppressed by glucocorticoid treatment (Abe, Nicholson, Liddle, Orth & Island, 1969; Thody & Plummer, 1973). In this study we report the absence of an effect on MSH secretion after adrenalectomy and dexamethasone treatment in the rat. Adult female Wistar rats were divided into three groups, A, B and C. When 10 weeks old, groups B and C were adrenalectomized. These rats then received 1% saline in place of tap water. Two weeks after adrenalectomy group C received daily, subcutaneous injections of 250 μg dexamethasone sodium phosphate (Organon Laboratories Ltd) in 0·9% saline. Groups A and B received saline only. Two weeks later the rats were anaesthetized with sodium pentobarbitone (Nembutal) and decapitated. Neck blood was collected in heparinized polystyrene tubes and