We developed and validated a new questionnaire for the assessment of the symptom profile and severity of generalised anxiety, the Generalised Anxiety Disorder Inventory (GADI). The 18-item scale (Argyropoulos et al, 2007, J Psychopharmacology, 21: 145-152) showed good reliability, convergent and divergent validity. The scale comprises three factors, relating to cognitive, somatic and sleep symptoms. It distinguishes accurately GAD patients from non-patient controls. The cognitive factor also distinguishes GAD from other anxiety disorders and depression. The sensitivity of the GADI to detect changes in symptom levels was tested in two experimental models of anxiety induction; the inhalation of 7.5% CO2 over a period of 20 minutes, which models generalised anxiety, and a single vital capacity inhalation of 35% CO2, which models panic anxiety (Bailey et al, 2005, Depression & Anxiety, 21: 18-25; Bailey et al, 2007, J Psychopharmacology, 21: 42-49). We found that the GADI was able to detect the differential drug effect of a benzodiazepine (alprazolam) and placebo in the anxiety induced by these tests in healthy volunteers.