In order to determine whether the characteristically attenuated cell mobilization after physical stress in patients with systemic lupus erythematosus (SLE) or sarcoidosis is disease specific or the result of lower tolerance for such stress, SLE and sarcoidosis patients as well as healthy volunteers were subjected to an acoustic stress model, independent of physical capacity. After a 10-min period of intermittent acoustic stress, healthy subjects showed significant increases in leucocyte and lymphocyte counts, marked relative elevations of B and T suppressor cytotoxic lymphocytes (P less than 0.01), and a relative reduction in T helper lymphocytes (P less than 0.01). By contrast, this degree of change was significantly less pronounced in the 14 female SLE patients studied (P less than 0.01) as compared with the healthy controls, but not in the 12 sarcoidosis patients tested. No dependence was found between the severity of disease or administration of corticosteroid therapy and cell mobilization. It is yet to be determined whether the attenuated response of SLE patients to stress is a consequence of pathophysiological mechanisms or plays an aetiopathogenic role in the course of the disease.