We investigated the lymphocyte interleukin-2 (IL-2) system, which is critically involved in lymphocyte activation, in patients with disorders or the hypothalamic-pituitary-adrenal (HPA) axis. Patients with Cushing's syndrome (n = 9) showed a significant (p < 0.05) inhibition of phytohemagglutinin (PHA)-stimulated IL-2 secretion by peripheral lymphocytes and a decrease of sensitivity to cortisol inhibition in vitro compared to normal subjects (n = 9). Circulating soluble interleukin-2 receptor (sIL-2R) levels were significantly decreased (p < 0.05), whereas no significant difference was observed in PHA-induced sIL-2R release in vitro. In patients with hypocortisolism (n = 12), in vitro IL-2 synthesis was increased compared to normal subjects and to patients with Cushing's syndrome (p < 0.01). In vitro sIL-2R release was significantly higher (p < 0.01) compared to patients with Cushing's syndrome. In contrast to patients with secondary adrenal insufficiency (n = 7), patients with an adrenal origin of hypocortisolism (Addison's disease, bilateral adrenalectomy; n = 5) showed significantly elevated circulating sIL-2R levels compared to normal subjects and patients with Cushing's syndrome (p < 0.005). There was no significant difference between the study groups in mitogen-induced DNA synthesis. This is the first description of alterations of cytokine secretion in patients with HPA axis disorders. The contrary effects of long-term hypercortisolism and insufficient or absent adrenal glucocorticoid secretion on IL-2-mediated lymphocyte activation could account for the immune states previously observed in these patients.