A reversed-phase HPLC method with UV detection at 252 nm is presented for the simultaneous determination of some tricyclic antidepressants (amitriptyline, imipramine) and neuroleptics (chlorprothixene, thioridazine) in their quaternary mixtures. Sample analysis was performed on a bonded reversed phase C-18, 5 microm, 250 x 4.6 mm ID (Lichrospher 100RP-18) column using acetonitrile and 0.01 M aqueous solution of triethylamine (1:1) as the mobile phase at 0.9 ml/min. The pH was adjusted to 2.7 with concentrated phosphoric acid. The retention time was for imipramine, amitriptyline, chlorprothixene, and thioridazine 5.8, 6.5, 8.3, 10.8 min, respectively. The linearity was obeyed up to 15 ppm for imipramine and amitriptyline, 12 ppm for chlorprothixene and 10 ppm for thioridazine. The presented method also allows the determination of the mentioned drugs individually in their pharmaceutical preparations.