A high-performance liquid chromatographic method is presented for the simultaneous identification and quantification of six commonly prescribed phenothiazines. Single-step extraction was achieved from alkaline samples with heptane - isoamyl alcohol (98.5 + 1.5), using prochlorperazine as an internal standard. A Spherisorb CN column was used, with a mobile phase of acetonitrile - acetate buffer (95 + 5). Detection was carried out at 254 nm.