In a depressed patient, the addition of citalopram 40-60 mg per day to treatment with amitriptyline 75 mg per day had no effect on the plasma levels of amitriptyline and nortriptyline, but it led to clinical improvement without the appearance of adverse effects. This and similar findings in four other patients comedicated with citalopram and amitriptyline (2 patients), clomipramine or maprotiline suggest that citalopram differs from other selective serotonin reuptake inhibitors, such as fluvoxamine and fluoxetine, which have been shown to increase tricyclic antidepressant plasma levels.