Steady-state plasma levels of mianserin, amitriptyline, and nortriptyline were determined by HPLC in two groups of elderly depressed patients who underwent a 5-week treatment with mianserin (60 mg/day in three oral doses) or amitriptyline (75 mg/day in three oral doses). Both treatments proved to be effective in reducing depressive symptoms. In the mianserin group, responder patients had steady-state plasma concentrations of mianserin higher than nonresponders. No relationship was found between amitriptyline, nortriptyline, or amitriptyline+nortriptyline plasma levels and clinical response in amitriptyline treated patients.