In order to assess the efficacy and tolerability of mirtazapine (Org 3770), 40 outpatients with a primary diagnosis of anxiety states [International Classification of Diseases (ICD-9)] were treated in a randomised, doubleblind, placebo-controlled, 4-week study (mirtazapine, n = 20; placebo, n = 20). Daily dosages of mirtazapine were 15 to 25mg. The dosage could be titrated upwards or downwards by 5 mg/day, depending on the clinical response or the development of adverse events, respectively. Anxiety symptoms were assessed at baseline and after 7, 14, 21 and 28 days of treatment using the Hamilton Anxiety Scale (HAMAS) and the Zung Anxiety Scale (ZAS); global functioning was assessed by the Global Assessment Scale (GAS). Biochemical, haematological and urinary variables were also measured. After 28 days of treatment, mirtazapine-treated patients experienced significantly greater improvement from baseline in overall anxiety symptoms and psychic anxiety (assessed by HAMAS and ZAS scores) and in global functioning (assessed by GAS scores) than placebo-treated patients. There were no clinically significant changes in biochemical, haematological or urinary variables with either treatment. Mirtazapine was well tolerated; only one patient withdrew from the study because of adverse events. Sedation was experienced significantly more often by mirtazapine-treated patients, while placebo-treated patients complained significantly more often of insomnia and crying, and had more sleep disturbances. In this study, mirtazapine appeared to be an effective and well tolerated treatment for patients with anxiety symptoms as a primary complaint.