Different physical, chemical and psychological stressors can provoke a unique but different endocrine response involving activation of the hypothalamo-pituitary-adrenal (HPA) axis. Inability of adequate compensatory reaction can lead to many disorders. The aim of our study was comparison of cortisol values in diseases provoked by various stressors. Our investigation included 34 posttraumatic stress disorder (PTSD) patients, as an example of disorder caused by extremely strong, acute stressful stimulus, 19 psoriatic patients, as an example of chronic stress stimulus and 17 healthy volunteers. In each patient we determined 24-hour urinary cortisol, serum cortisol at 8 a.m. and 5 p.m., and cortisol in dexamethasone suppression test by the standard radioimmunoassay (RIA) method. PTSD patients showed lower urinary 24-hour cortisol values, (361 +/- 28 nmol/24 h), "stronger" circadian rhythm of serum cortisol (595 +/- 57 nmol/l at 8 a.m. and 242 +/- 23 nmol/l at 5 p.m.) and attenuated suppression of cortisol in dexamethasone suppression test (197 +/- 45 nmol/l) in comparison to healthy volunteers (590 +/- 87 nmol/24 h urine, 590 +/- 32 nmol/l at 8 a.m., 402 +/- 31 nmol/l, and < 86 nmol/l in dexa test). Psoriatic patients showed markedly lower 24-hour cortisol values (150 +/- 98 nmol/24 h), even in comparison to PTSD patients, then serum cortisol values (404 +/- 138 nmol/l at 8 a.m., 187 +/- 80 nmol/l at 5 p.m.) and enhanced suppression of cortisol (23 +/- 5 nmol/l). The model of attenuated feedback inhibition in PTSD patients shows that they are unusually reactive to stress and represents an alternative model of acute stress reaction to extremely strong stressful stimulus. Unusually low cortisol values in psoriatic patients correlate to our hypothesis that in chronic stress-related disease, as psoriasis is, exists, by still undefined mechanism, altered HPA axis function, which is obviously incompetent to realise its immunoregulatory function, so consequentially, clinical signs of psoriasis persist.