Hypothalamic-pituitary-adrenal (HPA) axis sensitivity was investigated in 32 non-medicated patients with borderline personality disorder without comorbid post-traumatic syndromes and in 18 normal individuals using a modified dexamethasone suppression test (0.25 mg). Enhanced cortisol suppression was found in the patients v. controls (P<0.05) and the percentage of participant's with non-suppression was smaller in the patient (34%) than in the control group (89%) (P<0.01). Baseline cortisol levels in the patients were also lower than in the controls (P<0.05). The 0.25 mg dexamethasone suppression test reveals increased feedback inhibition of the HPA in borderline personality disorder.